Is the M1 bolt is better than the M1A1 bolt?

[buzz]

The M1A1 bolt has a fixed firing pin in the bolt face that fires the cartridge as the bolt closes fully.

 

The M1 bolt has a separate firing pin and hammer that are activated when the bolt closes fully.

 

 

It seems to me that the M1 bolt is better than the M1A1 bolt since the pin does not protrude from the bolt face until the bolt is fully forward and the hammer strikes a bridge in the receiver body.

 

This feature is not really 100% necessary but it would prevent an out-of-battery detonation of the cartridge if an out-of-spec cartridge jammed up in the chamber and refused to seat fully.

 

I know some have argued that an out-of-battery discharge is impossible because the cartridge slides up the feed ramp at an angle and does not present the primer to the firing pin.

 

However, as the cartridge moves a few millimeters into the chamber it must align itself with the axis of the bore to continue moving forward. It's impossible for the cartridge to slide down the chamber at an angle.

 

The 45 acp is a relatively low pressure cartridge and the Thompson is a very strong gun, so I think the danger associated with an out-of-battery discharge is low, but technically the M1 bolt would prevent it from happening.

 

 

I picked up an M1 bolt to try in my M1A1, I'm wondering if it would increase or decrease the ROF.

 

[whit]

Hi brother Buzz!

 

I also wonder the same thing...but I did the opposite - bought an M1A1 bolt for my M1

 

I am familiar with the particulars of complication, safety, etc.

But I remain unconvinced of the affect on rate-of-fire.

The discussions and experiments I've read seem imprecise at best.

 

With my ownership, I am hoping to ascertain whether there is a noticeable affect on ROF.

 

For a personal and peculiar desire, the slowest ROF interests me.

 

whit

[MauserMatt]

As far as my experiments have shown, the M1 bolt is faster than the M1A1 bolt. The M1 bolt is ever so slightly lighter in weight than the M1A1 bolt and apparently makes up for a noticeable difference. Thus slowing the ROF for the M1A1.

 

Here's two of my YouTube videos to show the difference. The gun is an M1 and I purchased an M1A1 parts kit for spares.

 

<-- M1A1 bolt

 

<-- M1 bolt Edited April 26, 2016 by MauserMatt

[whit]

Thanks MauserMatt!

 

Very convincing. I assume that was with the same ammo?

 

I tend to use lower powered ammo (i.e. Winchester White Box) with the belief that it will be less stress on the gun and also lower ROF.

 

Of course some might argue that less recoil means faster (sooner) bolt return and thus higher ROF.

 

This discussion tends to be a can of worms, I know.

 

But what is often omitted is the "rate of recoil"

I'm not sure that it's linear.

[MauserMatt]

Ah yeah, forgot that detail. Same ammo. I think in both videos it was CCI Blazer Brass with large primers.

 

Though I've shot plenty of machineguns, courtesy of the US Army, this is the first one I've ever owned and could play around with.. So it's really been very interesting, to me, how many variances there are in different brands of ammo. Owning a machinegun really opens your eyes to consistency of powder burn rates... Or lack thereof... Haha...

[TSMGguy]

The M1A1 bolt was thoroughly tested before it was adopted. There's no danger of a cartridge firing before the M1A1 bolt is fully into battery. The only reason to prefer one type of bolt over the other is that the M1 bolt gives a faster rate of fire. In my own M1, the ROF with the M1 bolt is a precisely timed 750 rounds per minute. It's 650 RPM with an M1A1 bolt.

[buzz]

I tend to prefer a higher ROF, I can shoot a faster gun more accurately. Up to a point anyway.

 

I have found that weaker ammo slows the ROF down. If you run half a mag of weak ammo followed by half a mag of hot ammo, the effect is very noticeable.

 

Remington UMC green box or yellow box ammo is loaded very weak if you want to try it.

Edited April 27, 2016 by buzz

[Paladin601]

Interesting topic,

 

My belief that anytime you can reduce the number of parts and still accomplish the same purpose the better. I like the fixed firing pin. Rate of fire can be changed readily with proper trigger control

Edited April 27, 2016 by Paladin601

[hawksnest]

Sitting on the sidelines waiting for the argument the M-1 bolt is safer than the M-1A1 bolt. Not necessarily so. Had a lead reload fail to fully seat in the chamber due to a lead ring left from the previous lead round. (The friend who reloaded my ammo didn't have his die adjusted right when seating the lead projectile and crimping the case). The round went off and blew the rim off the bolt face, the floor plate blew out of the magazine and the front part of the case was left in the chamber. I think the inertia of the M-1 bolt going forward while on full auto was enough for the firing pin to move forward against the tension firing pin spring. That's may belief - YMMV. Now I went and did it!

[TSMGguy]

We have to be careful not to blame the original design when the problem was bad reloads.

[buzz]

Well, the whole point of the separate hammer and firing pin is to address a problem like a bad cartridge or dirty chamber.

 

If the separate hammer and firing pin doesn't keep a bad round from detonating, then they're not worth the extra cost to machine them.

 

 

It would be interesting to jam a empty (but primered) case in the chamber a few millimeters shy of being fully seated and then let the M1 bolt slam home on the jammed case and see if the inertia of the firing pin pops the primer.

 

Or see what happens if the hammer was to very lightly tap the receiver due to a jammed cartridge, see if that put enough energy into the firing pin to pop the primer.

 

 

I agree with Paladin, the best design is the one that can accomplish the task with the fewest parts. For obvious reasons.

 

I personally regard the M1A1 as the best version of the Thompson, the gun was simplified in a clever and efficient way that resulted in a far better weapon.

 

Of course gun collectors feel differently, they love fancy features and bells and whistles.

 

 

The reason I posted this thread is because I had purchased a new barrel for my UZI and had a couple of rounds jam up and detonate out of battery.

 

If the cartridge jams about halfway into the chamber, the UZI bolt with its fixed firing pin will pop the primer.

 

The rounds just burst and blew brass chunks out the ejection port with no harm to the gun.

[Paladin601]

Look at cars, most people want all the bells and whistles they can afford.

I think that the M1A1 is a great gun, however I would ad 2 things to it to make it better, a top mounted bolt handle and detachable but stock. Keeping it simple is always the best route, cost, easily repaired and "I feel" more durable.