WTK: reasons for late Type V op slide changes

[Prairie Fire]

Howdy all. I haven't posted here for about fifteen years.

I've had a Winchester-based rebuilt carbine since the late '80s. It's a Blue Sky Import. Gun has a Type IV slide and a flat bolt.

Recently I found the site www.uscarbinecal30.com. In the description of slide types, it was mentioned that later Type V slides (drawing # 716091), and all Type VI slides were cut .040" forward in order to increase dwell time, which had the effect of reducing chamber flash upon extraction. Round bolts (sans "X") were changed in dimension at the right lug in order to match the slide.

My question is, how big of a problem was chamber flash? I'm assuming that dimensional changes to parts during wartime production were not done for whimsical reasons. On the other hand, since earlier slide types were not replaced wholesale during the rebuild process, maybe chamber flash was a more minor problem (not as important, say, as the grinding of the tails of firing pins, or safety and mag catch shape changes, or the rear sight change.)

I was wondering if anybody here knows more of the story behind the reason why a wartime change was made in order to reduce chamber flash.

Personally, on a shooter, I'd prefer to not risk an eyeball full of flaming WW-296 if I had the sudden need to shoot without eyepro. My gun dirties cases bigtime, but I've not experienced incomplete ignition coming out with the case. Unusually dirty cases might also be an unrelated thing.

Thanks for looking.

[Sunray]

"...an eyeball full of flaming..." You should be wearing eye protection when shooting any firearm, at all times.
Part dimensions were usually altered to facilitate ease of manufacturing. Round bolts, for example, are easier to make than the flat. Lotta milling involved with a flat bolt. They supposedly made FA fire in M2's work better too.
Never seen nor heard of anything remotely like a chamber flash. The only time there'd be anything like incomplete ignition is with substandard ammo. Gun powder doesn't fail to burn unless it got wet or was substandard to start.

[BrianQ]

Round bolts weren't cheaper to make. That's a myth perpetuated by people that are generally clueless. It sound good but has no basis in reality. Flat bolts were not forged into a round shape just to have the top portion milled off. They were forged with a flat top and milled to the desired dimensions. Raw round bolt forgings were round then milled to the desired dimensions. Ask a machinist which raw forging would be cheaper and easier to mill to the proper dimensions along the body.

As far as the increased dwell modifications on the later slides they were done to increase the dwell time which improved extraction and lessened the stress on the bolt lugs. The reduced chamber flash was an unintended secondary benefit to the increased dwell. Some earlier slide types can also be observed with the increased dwell modifications.

BTW I did the research and wrote the article the information on the web page is based on.