M1928/M1A1 Bolt

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I'm not an engineer so please make note of the source.

 

I own a STEN MKII and it's bolt has a fixed firing pin similar to the M1A1 bolt. It is my understanding that part of the energy of the bolt slamming into the breech face of the barrel chamber is absorbed in the STEN firing cycle because of API (Advanced Primer Ignition). Basically, the cartridge is beginning the ignition process just as it is being fully seated which has the net effect of softening the inertia of the bolt slamming into the breech face of the barrel.

 

Since the M1A1 bolt has a fixed firing pin, wouldn't it also experience API, which in this instance would act as an energy reducer compared to a 45ACP round igniting on a fully closed chamber such as occurs in the 1928 as well as the M1 bolt versions which use a hammer and firing pin? And consequently, couldn't this help in the reduction of stress from the bolt hitting the rear of the receiver if less energy is being transferred to the bolt during the moment of ignition?

[mohawk64]

The 1928 / M1 bolt does use a hammer - firing pin. But the timing ( from what little I know ) seems to be the same as the m1a1.

[reconbob]

Many people do not believe in API - where the cartridge is ignited split

seconds before the bolt is fully home with the final forward movement of the

bolt acting as a "shock absorber" for the recoil.

The reason the semi autonThompson has such very heavy recoil springs

is because the cartridge is ignited with the bolt at a dead stop and does dot

have the benefit of the API effect.

The question is how hard do the different bolts hit the back of the receiver.

 

Bob

[deerslayer]

I've been reading those and started a new post.

[Wayne W]

This may not be of much help or maybe it will jog someones memory.

IIRC A few years ago Doug Richardson wrote something about making some TSMG bolts that were in the M1 style that would work in the 21/28 receivers. 9mm and 45 ACP, relocated recoil spring hole and a few other changes.

I did a search in this forum and didn't find anything so it must have been in the blog on his website. Maybe someone saved a copy of the blog somewhere.

 

reconbob, yes I would be interested in one of these bolts if made in 9mm. Maybe you could make some ejectors that are just a smidge longer to use with 9mm.