Question on Semi 42

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Littledan65
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Question on Semi 42

Postby Littledan65 » Mon Jun 01, 2015 11:40 pm

I'm getting ready to fire my build. In cycling some dummy rounds, sometimes the bolt will hang up about an inch or so from full lock. This got me thinking. What would keep the first gen BRP firing pin from detonating a round out of battery? It seems I can push the firing pin out of the bolt head even if the rollers are in. What would prevent the OOB firing of a round if for some reason the bolt is not fully in the breech? I'm just concerned as I have a ton of time into getting to this point and don't want to take any chances.

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Re: Question on Semi 42

Postby usmc8488 » Tue Jun 02, 2015 10:48 am

Nothing... I had an out of battery detonation on my first build using the BRP bolt, it was about round 20 or so. The result was a bent barrel door, broken main spring and the back of the bolt where the main spring was cracked.

Figure out why it is hanging up. the bolt should slide freely. In my case it was a rail alignment issue with the trunion.

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Re: Question on Semi 42

Postby Littledan65 » Tue Jun 02, 2015 11:02 am

I did a little more work on the AR hammer. Fired about 6 rounds and they all chamber well. It's short cycling though, need to figure that out. I may have to use the MG3 booster since I'm shooting 308 Win. Also getting pretty hard primer strikes so I guess I'll try putting a few small washers in there to back up the firing pin?

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Re: Question on Semi 42

Postby JBaum » Tue Jun 02, 2015 11:28 am

An MG3 booster will likely give you less recoil than you have now.

You need a nozzle with a smaller hole. What size nozzle are you using now? Are you shooting 8mm or .308?

Have you lubricated the rails and polished the hammer so it doesn't drag on the bolt during recoil?

You don't have enough recoil for the amount of friction you have. Reduce friction, or increase recoil. Doing #1 first is better.
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Littledan65
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Re: Question on Semi 42

Postby Littledan65 » Wed Jun 03, 2015 9:30 am

I'm shooting .308 with the original 8mm booster. I would have thought the smaller round would have had a booster to provide more recoil?

The bolt slides like butter and I did do some polishing on the hammer. I agree though, need to reduce friction. I may grease everything up too. It's all new and the parts are getting used to being next to each other. Hopefully running some rounds through it will help.

Has anyone had to machine some off of the semi auto blocker for spring clearance? This seems to be the area I have the most resistance.

How can you tell which size nozzle you have?

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Re: Question on Semi 42

Postby drooling idiot » Wed Jun 03, 2015 1:06 pm

you'll need to silver solder a stop on the front of that pin.
It needs to hit the back of the striker before the firing pin protrudes until the rollers are out and locked.
The original pin length plus .44" works for all my builds.

I can't believe anyone would still be selling such a dangerous design still after years of having a safe design free to copy. Is this pin old?

:search my old posts the designs should still be here. be safe
"good , bad, .....I'm the man with the gun."

Its amazing anything works right around here with a bunch of
over-age juvenile delinquents running the place.

Littledan65
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Re: Question on Semi 42

Postby Littledan65 » Wed Jun 03, 2015 1:41 pm

Wow, I actually just bought it new. Should I just go with the gen 2 pin, or does it have the same problem?

$30 vs OOB is well worth it. I guess I could turn my own pin, but thought buying one was the safe route. So much for thinking.

I was a little suspicious of this design in doing the research and studying the original design.

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Re: Question on Semi 42

Postby Littledan65 » Sun Jun 07, 2015 9:48 pm

O.K, I think I know the problem. I was using oakrodents tutorial and drilled the striker. He builds a different version of a firing pin. I shouldn't have drilled the striker. I'll get a new one and it should work.


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