View Full Version : The value of a headspace gauge
I bought a 30-06 headspace field gauge to check my newly acquired Winchester M1917 in order to see if it was safe to shoot. I also bought a Winchester bolt last week on eBay to replace the Eddystone bolt that came with the rifle so I had two bolts to test. The Eddystone bolt passed and the Winchester bolt failed. The eBay seller agreed to take the Winchester bolt back and refund my payment. The $29 I spent for the headspace field gauge was probably the best investment I've made in a while. It also points out the fact that excessive headspace isn't always caused by a worn barrel.
Cosine26
02-21-2016, 10:58
Before you send the Winchester bolt back let me send you this article on headspace measurement of the M1917.
FWIW
M1917 Headspace Measurement
In past posts I have seen several discussions concerning measurement of headspace in a M1917. This has been the subject of continuing discussion for a number of years. Excessive headspace of M1917’s was discussed after WWI when the M1917 was released for sale and again after WWII when the M1917 was again released for sale. The M1917 bolt lug design differs from the M1903, M54, M70, M98, etc. Rather than trying to discuss it as an amateur, I researched the matter and found the opinion of an expert. Remember that after WWI Remington used “left over” M1917 action to create the various versions of the Remington Model 30 rifle. The bolt and receiver of the M30 with cosmetic modifications duplicates that of the M1917. The question arose when an attempt was made to measure the headspace of a Remington 30 using a cartridge and some metal shims. Using this method it was determined that the headspace of a Remington 30 was excessive. The rifle was returned to Remington and was found to be well within spec. The following is a letter from the Works Superintendent of the Remington Arms factory. This information comes from “The Dope Bag” appearing in the AMERICAN RIFLEMAN magazine for February 1934, p 32. I quote as follows”
“A review of the correspondence between yourself, Mr. Hadley, and others Indicates that your method of headspace measurement is with a cartridge or dummy cartridge and shims of known thickness. In view of this procedure of headspace measurement, we wish to call to your attention to the locking cam arrangement of our Model 30 as compared to the locking cam arrangement of the Springfield. Figures which are given below are approximate but are sufficiently close to demonstrate the comparison.
“In the Springfield the bolt lugs ride the locking cam having a lead of 1.5” per revolution, through a swing of approximately 37 degrees, after which the flat rear face of the bolt lugs contacts the flat face of the locking shoulders of the receiver.
In the Model 30 the bolt lugs ride a lead cam having a lead of 1.5” per ‘rev’ through a swing of only 20 degrees, after which the ‘cam-cut’ rear faces of the bolt lugs contact the locking cams on the locking shoulders of the receiver and move through of a swing of approximately 70 degrees on these locking cams, which have a lead of 0.14” per ‘rev’. The power of the locking cams on the Model 30, as compared to the locking cams on the Springfield may be said to be in the ratio of 1.5 to 0.14; that is the power of the locking cam on the Model 30 is 1.5/0.14 or 10.7 times as much as the power of the locking cam on the Springfield. In other words, on the Model 30 rifle to close the bolt against resistance requires a force approximately one tenth of that required by the Springfield
“This proposition may be stated in a different manner as follows:
“The Springfield has a lead cam of 1.5’ through a swing of 37 degrees and no locking cam.
“ The Model 30 has a lead cam of 1.5” lead operating through a swing of 20 degrees and then a locking cam of 0.14” lead operating through a swing of 70 degrees.
“In the Springfield the bolt swings through approximately 37 degrees on a 1.5” cam to get to the limit of full forward linear travel. The remaining swing of the bolt in the closed position to its closed position is on flat surfaces of bolt lug and receiver and there is no forward travel after completion of the 37 degree swing
“In the Model 30 the bolt swings through approximately 20 degrees on a 1.5’ lead cam and then through 70 degrees on a 0.14” locking cam to get to the limit of full forward linear travel.”
There is further discussion in which Mr. Brown states:
“We believe the power of this locking cam to be an advantage in the use of the gun, since it provides considerable power to close over a cartridge which may be mutilated or too long. We believe also that the locking cams on the Model 30 permit easier opening after firing.
H.A. Brown”
* I realize that this is a long discussion, but I think that it points out how incorrect headspace measurements can be made in the M1917/M30 type of action. The bolt should be stripped and only light finger pressure exerted when measuring headspace.
Hope this is informative
I've read that old and interesting article concerning excessive headspace several times on this and other forums and it is fascinating from an engineering perspective. Thanks for reminding me. However, the condition of the Winchester bolt was a problem from the beginning. It shows a lot of wear along with corrosion damage to the body which the eBay seller didn't include in his description. The head of the bolt was slightly distorted like it was dropped on a hard surface. I was considering returning it for a refund when the headspace field gauge arrived in the mail yesterday and convinced me to return it and keep looking.
I had a gunsmith test headspace (with the Eddystone bolt) on the day I bought the M1917 with a no-go gauge and the bolt closed completely on the no-go gauge. Field gauges are a few thousands longer but he didn't have one to try. I can't imagine a gunsmith without a 30-06 field gauge. It made me wonder if I had made an expensive mistake since I planned to shoot the rifle. The M1917 headspace information on this and other gun forums is beyond valuable since it fully explains the spacious headspace situation that's typical in military rifles.
Another note on headspace. I bought a sweet shooting 1944 Enfield No. 4 Mk 1 .303 cal. made by Savage a few years ago and it closes easily on the .303 headspace field gauge which indicates failure. The bolt heads on Enfields come in several sizes which can be changed if headspace becomes excessive. My Enfield has a no. 2 head on the bolt and I've been searching unsuccessfully for a no. 3 head for more than a year. Lots of no. 0s, 1s and 2s but no 3s. That hasn't stopped me from shooting the rifle which is very accurate. I shoot PPU .303 British and reload my own. The PPU cases weigh a little more than cases made by Winchester and Remington and may be close to military grade. For cases shot in overly spaceous chambers, it's important to only resize the case necks. Using a full length die that resizes the neck and case body every reload causes unwanted expansion-contraction which can weaken the brass and cause early case-head separation. So far, I've shot a few hundred mostly reloaded PPU cartridges through my No. 4 without a case head separation. It's important to only shoot the reloaded ammo in the same rifle.
While that article is interesting, it does not make clear how to check head space on a 1917 using the current tools.
First, you want to remove the firing pin. Let me know if you don't know how to do that.
The best experts also say to remove the extractor but I have not found that to be needed.
If you don't have a field gauge, put a piece of freezer tape on the back of the no go gauge.
Then load the gauge into the magazine, push the bolt forward and finagle the gauge base groves into the extractor and once is caught like a bullet, then carefully advance it and gently very gently close the bolt.
If its ok, what you will find is as you get to the last bit or bolt closure you will get resistance. It may even be early in the closure depending on the bolt machining (they do vary some)
If its in that range you are good.
I would also urge anyone working with these rifles to get the Steven Mathews TE MW gauges for the 1903. It works on the 1917, the Throat Erosion part is not calibrated per Steve, but its close enough to tell you roughly what you have.
My guns all come in within about 1/2 a reading for the MW. If the muzzle is 3, then the TE will get 3.5 or a bit less and my take is that the TE may be off just a bit, if calibrated for a 1917 it would read more like 3.25 ore maybe even 3 for the TE
RC20,
I have pulled the striker assembly and removed the extractor spring before testing headspace because it's a fairly simple procedure. The bolt closed about 80 per cent before coming in contact with the base of the field gauge. I made a tool to pull the striker by cutting away a portion of a metal washer with a Dremel tool. I have thought seriously about measuring TE and MW and will look into that next. The bore looks clean with strong rifling throughout the length of the barrel however, I'm in no hurry to shoot this old boy. I'll do everything right.
Merc
JB White
03-05-2016, 02:52
Merc, back to your Lee Enfield. Are you aware there are 2 different sets of specs for HS? The American SAAMI gauges are off by at least .004 to the British military spec. You need a .074 FR, not a .070.
Also, the swapping of bolt heads is a US based fallacy. The boltheads are different lengths for manufacturing purposes and decreased assembly time. (They used to have to stone each head into spec) The heads also index differently as far as overtravel, so you might have to buy several rare bits before finding one that rotates correctly.
British wartime specs were much more generous in the HS department. If you rifle is shooting well then enjoy it as it is.
JB,
Thanks for the info. That answers a few questions.
I had a gunsmith visually inspect the Lee Enfield No. 4 Mk 1 rifle shortly after acquiring it because the stock was stenciled in big letters: BLR (Beyond Local Repair). So, at some point in its life, it needed to be sent back to the arsenal for service. I understand they usually removed the lettering once repairs were performed so I have to assume that the repairs were not performed. I suppose it's possible that BLR could have meant it was designated for a routine post-war refurb prior to continuing service but I'll obviously never know for sure.
The smith said the action and the rifling looked fine but he didn't have a .070" HS field gauge to test headspace and suggested getting one. So, I ordered one and tried it. The bolt easily closed 100% on the .070" HS field gauge.
It's great to know what the British HS specs are. I tried something after reading your message. Cellophane tape measures .002" thick by my 0-1" micrometer. I added two layers of cellophane tape to the end of the .070" HS field gauge thereby increasing the length to .074". The bolt now closes to about 80% on a .074" gauge which is well within the British specs. (It closed to about 90% with just one layer of tape.) I'll check around to see if someone makes a .074" HS gauge.
I've shot a several hundred rounds through the rifle since acquiring it a couple years ago. It's surprisingly accurate for a 72 year old boy. I haven't had any case problems so the BLR designation will continue to remain a mystery for now.
Just to indicate the demand for No. 3 heads for a Lee Enfield No. 4 Mk 1, there's one currently being offered on eBay for $180. Since most No. 4 Mk 1 rifles usually sell for double that price, I suspect the head will be there for a while. Most 0s, 1s and 2s go for a small fraction of that price.
Why are there are two different HS specs for the No. 4 Mk 1? It's a British rifle. The HS specs should be British.
Thanks again, worrying over nothing.
Merc
Someone put in a lot of effort to post a good explanation on head space and head clearance for .303 British although it could apply to all. Those of us who reload our ammo will get a good reason to resize only the necks of the cases for extending case life.
http://parallaxscurioandrelicfirearmsforums.yuku.com/topic/3361/t/Headspace-101-for-303-s.html#.Vtwg5f_2bIV
JB White
03-06-2016, 08:22
This should be addressed on a different board, but since we're both here...
Why are there are two different HS specs for the No. 4 Mk 1? It's a British rifle. The HS specs should be British.
Let's eliminate the SAAMI part first. (The Readers Digest version)Those specs are for sporting rifles where owners tend to reload commercial brass. There is a margin of liability built in there.
Military rifles are in a different realm. Chambers are generous to take into account water and mud etc. Ammo is set to spec using heavier brass and there are no provisions for an individuals reloads. The .074 spec has its own safety margin where the rifle is safe to operate without fear of malfunctions.
Emergency Wartime Spec was set for older rifles still in service. The FR can be up to .080 (.082 depending upon the source cited) and the Lee rifle will still function without mishap. *No reloads as the fired brass has been stretched to or beyond its working limits.
The 303 headspaces on the rim which makes it much more forgiving than a rimless cartridge. Neck sizing only and keeping the brass segregated for the individual rifle helps to compensate by working the brass less, thus extending case life into a normal range. It isn't a fix for generous headspace. Only an economical work-around for us shooters.
The BLR marking could mean anything but usually means something is getting tired within the action. Could be the lugs have taken a set too far back? That might explain the point of resistance being farther through the travel than normal. You're still good since I doubt you'll be running the number of rounds through it as it might see in Cadet service.
The action could be salvageable for service with a complete factory inspection, a bit of dressing, and a new bolt assembly fitted. We don't like to go there because if an armorer deemed it questionable with all his tools, parts, and experience, then we shouldn't question his judgments. At least it's not BER which is 'Beyond Economic Repair' meaning nearly the same as......scrap.
Thinking I could have sold you a NOS #3 bolthead while rubbing my grubby paws together dreaming about how many pizzas that could buy. That wouldn't be right. ;)
I agree about this topic belonging on a different board. The M1917 guys shouldn't mind too much since head space debates are universally applicable.
One more question:
You mentioned several head space dimensions. Which of the .303 British HS gauge dimensions would be considered a field gauge dimension by us yanks? .074?
Thanks again for the info. I appreciate the wealth of knowledge that's shared on this and other gun forums.
Merc
I have a M1917 rifle with a chamber that is .002” longer than a filed reject length gage. When sizing cases for that chamber I use 280 Remington cases. The 280 Remington case is longer than the 30/06 case from the shoulder of the case to the case head by .051”. I do not find it necessary to fire form, I form first then fire.
When sizing a case for the long chamber I adjust the die .014” off the shell holder then size the case, I could use a 30/06 forming/trim die first then size but I do not find it necessary. I do believe head space gages are nice but as long as they keep installing threads in my presses and on my dies I will continue to off set the length of the chamber with the length of the case.
F. Guffey
I measure chamber length in thousandths. I do not measure the length of the chamber in go-gage length, I do not measure the length of the chamber in no-go-gage length, I do not measure the length of the chamber in field gage length, and I measure the length of the chamber in thousandths.
And then there is the short chamber. I was thinking by now someone could measure bolt travel/advance in thousandths as in from open to close.
F. Guffey
There is a cute little saying that goes around gun smithing forums that suggest purchasing a bucket of bolts is better
than buying one bolt. Seems the thinking suggest if the first bolt does not reduce the length of the chamber from the shoulder to the bolt face all that is necessary to do is reach for another bolt from the bucket.
A few years ago I purchased a mill from a collector, builder of correct military rifles/reloader. He was having trouble reducing the length of the chamber of a period correct 03 Rock Island. He said he was trying to get help from one the reloading forums. I ask which one; he told me, I suggest he forget about getting help from that forum because I thought it was too social dysfunctional.
I did tell him it was his luck day because I determine head space/the length of the chamber three different ways without a head space gage. In a few minutes I determine the length of his chamber was .0075” longer than a minimum length/full length sized case or .0025” longer than a go-gage length chamber.
It was about that lime he handed me a 30/06 go-gage from a box of 20 head space gages. Nice, we all know the bolt will close on a go-gage. He then handed me a no go-gage for the 30/06 chamber. I told him we both knew the bolt would not close on a no go-gage unless the chamber is longer than a no go-gage. I told him the chamber was .0025” shorter than a no go-gage length gage.
Then came time to reduce the length of the chamber; I offered to form cases that would fit. He wanted to use a bolt; problem, he had no fewer than 100 03 bolts and none of them would reduce the length of the chamber .0025” but I offered to check every bolt he had warning him this period correct rifle required a straight handle bolt.
I informed him I have 35 06 replacement bolts for the 03A3 and none of them have a straight handle and I knew none of my bolts would reduce the length of his chamber by .0025” but I did not mind trying.
He was going to use new factory R-P ammo for testing the rifle.
F. Guffey
I take the military brass situation in general with a lot of grains of powder
In 30-06, I see it weight less than FC and RP.
Less weight, more space. A member of another forum had a rule of thumb that it took 17 gr case weight to equal a grain of powder.
Other brass of course may vary and I may not have seen all the 30-06 variations, digital scale is a great asset for quick checks though.
If I had a extra large chamber I would consider FC brass as its softer, probably contour to the chamber better and then deal with re-size to suit.
In 30-06, I see it weight less than FC and RP.
I am trying to determine what 'it' is. It weighs less than FC and RP? IF FC and RP are 30/06 cases; what is 'it'? Straight across the board Winchester military 30/06 cases weighed less than any other 30/06 military case; Winchester 30/06 cases were stamped WW, WCC, WRA and Winchester.
F. Guffey
FC are the heaviest. From memory of 205 gr.
RP the next, something around 195 gr.
I like RP a lot, it seems to be in between soft and hard, lasts well etc. Opinion and feeling, I can't prove it.
Military is down in the 185 or 190 gr.
FP is very soft, I think (opinion) it would fire form better, its also throw away as I have yet to be able to keep it more than about 8 rounds even with carful shoulder setup (based on the fired shoulder not any default dies setup.
Along with my brother, we have measured something like 12 Model of 1917s. All were about the far end of field reject, all shoot just fine.
As they are military we accept them for what they are and have fun shooting them.
Along with my brother, we have measured something like 12 Model of 1917s. All were about the far end of field reject, all shoot just fine.
And no one has a clue as to why? A bunch of smiths got to gather and found someone to blame it on. This stuff does not lock me up and I find no reason to make up stories, for me it is not challenging, if I have a rifle with a long chamber I form cases to fit. For most that is a complicated process because they only have cases available to them that manufacturers make available. I purchases cases that have been fired in long/trashy old chambers, when culling the cases at the range I cull the cases, I only purchases cases that are long from the shoulder to the case head. I use the length of the case from the shoulder to the case head to off set the length of the chamber.
I noticed you did not list the length of the chamber in thousandths, you only mentioned field reject gage. I have a M1917 that has a chamber that is .016" longer than a minimum length/full length sized/over the counter/new round; what does that mean? It means a new factory over the counter round has .016" clearance between the shoulder of the case and shoulder of the chamber. If I fired cases that were go-gage length from the shoulder to the case head I would have .011" clearance. But, because this stuff does not lock me up I use 280 Remington cases, when sizing the 280 Remington cases I adjust the die off of the shell holder .014" with a feeler gage and then size the case. After sizing and trimming I load and then chamber the case, after chambering I have the magic .002" clearance between the shoulder of the case and shoulder of the chamber. I have asked many times where did the magic .002" come from? Almost all reloaders respond with "I bump...."
.016"? Reloaders believe the case has head space, they believe .016" is too much head space and the case will have case head separation. And then I say the shoulder on my 30/06 cases do not move when fired in my M1917 and none of them understand what I am talking about.
F. Guffey
The head space thing has gotten to be quite the myth. I have done a standard write-up that I think it clear.
If the headspace is too long the gun won't fire. Shell moves forward with the firing pin hit and simply won't shoot.
If its marginal (per SAMMI) then it will fire fine, blow the case out and if you do a minimum shoulder bump back you have a fire formed case that is fine.
303 had generous head space and chambers. You cant reload it more than 3 times, it does not kill anyone.
If its too short no new brass will fit. Self fulfilling you can't shoot it
In between its also not an issue.
You get better accuracy with fire formed to the chamber and minimum bump back but I suspect that's under 1/2 MOA
All my 1917s push the very limit of field reject. They just get their own brass.
The head space thing has gotten to be quite the myth. I have done a standard write-up that I think it clear.
If the headspace is too long the gun won't fire. Shell moves forward with the firing pin hit and simply won't shoot.
[QUOTE]I have done a standard write-up that I think it clear You think it clear? I have always said there are a lot of events that happen between pulling the trigger and the bullet leaving the barrel reloaders simply do not understand. "If it is too long?" Meaning the chamber from the shoulder to the bolt face? And you done a standard write=up?
I chambered a round in a rifle, I pulled the trigger and the bullet left the barrel. I ejected the case, the case was ejected with just a hint of a neck, the shoulder on my case did not move. I could ask "What does that mean"? Because of the failure of the reloader to understand the events between pulling the trigger and the bullet leaving the barrel asking the question "what does that mean" is a wasted effort.
The case that was ejected with the hint of a neck: I moved the shoulder on a chamber forward .127" forward meaning I increases the distance from the shoulder to the bolt face .127": After increasing the length of the chamber I chambered a case that was shorter from the shoulder to the case head (minimum length/full length sized case in the long chamber, closed the bolt and then pulled the trigger.
The case, bullet, powder and primer did not out run the firing pin, the case did not move and because of this miracle the case head did not move from the bolt face. My firing pin busted the primer before anything took off for the front of the chamber. I know that is what happened, the case proves the case did not take off for the front of the chamber. I do not make this stuff up; reloaders believe they can move the shoulder back, they believe they can bump the shoulder back. I can't, it all goes back to reloaders not understanding what happens between pulling the trigger and the bullet leaving the barrel.
F. Guffey
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