Light primer strikes with JP bolt assembly in LMT MWS

[bllistc]

I got a JP high pressure bolt/firing pin for my LMT and I’m getting light primer strikes. I’m shooting 6.5 CM with small rifle primers loaded with federal 205M primers. The first 100 or so rounds I didn’t have any light strikes. Taking a class this weekend and I’ve gotten 25 light primer strikes out of about 150 rounds. I cleaned the BCG and got another 20 rounds or so before it started happening again. Any ideas what’s going on?

I’ve never had this issue with the factory bolt assembly shooting .308 or 6.5 CM.

 

[bigjake83]

I'm pretty sure the JP Bolts are NOT compatible with the LMT Carrier, I know for a fact the a LMT 6.5CM Bolt is to big to fit in a JP Large Frame LMOS Carrier.

 

[bllistc]

I'm pretty sure the JP Bolts are NOT compatible with the LMT Carrier, I know for a fact the a LMT 6.5CM Bolt is to big to fit in a JP Large Frame LMOS Carrier.

Emailed JP before getting it and they said it is compatible. Like I said it worked perfectly for the first 100 or so rounds.

 

[bigjake83]

Did you bother to check headspace?
The only other possibility would be a issue with your trigger, or some brass shavings inside the bolt where the firing pin travels.

 

[bllistc]

Did you bother to check headspace?
The only other possibility would be a issue with your trigger, or some brass shavings inside the bolt where the firing pin travels.

No I didn't think to cus I never do for ARs but thats probably a good idea. Damn I feel dumb.

 

[oldfatguy]

Was getting a few light primer strikes with light trigger & hammer springs in a 9mm PCC shooting Tulammo steel cased. Same rounds fired just fine in another PCC with “standard” springs.

OFG

 

[bonifacio]

What trigger do you have?

 

[Merle]

Doesn't LMT use the smaller diameter firing pin/bolt hole from the factory???

 

[bllistc]

What trigger do you have?

it’s the factory trigger.
@Merle no they don’t.

 

[bllistc]

Ok so I figured out what’s going on and yes I’m an idiot and should’ve done more research rather than just relying on that the manufacturer told me.
The JP bolt is for DPMS/LR308 pattern rifles. The LMT MWS is an Armalite/SR25 pattern. I’ve seen threads where people swapped BCGs between the two and had their rifles explode so I’m counting myself damn lucky I got away unscathed. Lesson learned.

 

[flyfisherman246]

How were they exploding? Bad headspace between the different rifles? I’ve measured headspace between and aero m5 bolt which is dpms pattern and lmt mws bolt and they were exactly the same. And they ran fine. What issues could it cause?

 

[bigjake83]

Ok so I figured out what’s going on and yes I’m an idiot and should’ve done more research rather than just relying on that the manufacturer told me.
The JP bolt is for DPMS/LR308 pattern rifles. The LMT MWS is an Armalite/SR25 pattern. I’ve seen threads where people swapped BCGs between the two and had their rifles explode so I’m counting myself damn lucky I got away unscathed. Lesson learned.

 

[bllistc]

How were they exploding? Bad headspace between the different rifles? I’ve measured headspace between and aero m5 bolt which is dpms pattern and lmt mws bolt and they were exactly the same. And they ran fine. What issues could it cause?

Headspace would be my guess. I ordered gauges so I’ll check headspace when they get in. But there was a thread on here about a guy who put a DPMS BCG in an armalite rifle and it exploded.

 

[Merle]

it’s the factory trigger.
@Merle no they don’t.

I just measured my MWS firing pin and it's .068" in diameter, which is the Armalite size. Armalite was always "high pressure". Did you measure your LMT bolt and firing pin before buying the JP bolt?

 

[bllistc]

Hmm. Interesting. No I didn’t measure the firing pin but the firing pin hole is a larger diameter than the JP bolt. That also contributes to primer flow and pressure signs at low charge weights with small primer brass. All of which is what I was getting.

 

[flyfisherman246]

Ive used a LMT MWS bolt in an Aero m5 bolt carrier, cam pin, and firing pin just fine. I'm curious where your issue comes from.

 

[357Max]

What is your firing pin protrusion with the JP bolt/pin vs. the LMT bolt/pin?

Measure the length of the LMT firing pin from tip to the shoulder where it contacts the back of carrier & compare that to the JP? This may be your issue.
The pin protrusion is set by the shoulder contact of the pin to back of carrier. Since there's no mil spec on large frames there is no guarantee the LMT carrier uses the same length as JP. Will it physically fit vs will it correctly function in a large frame are 2 very different questions.

I've found 3 blueprints for large frames (Armalite & DPMS) that have 3 different locations for the fire control group from the front take down pin.
The above indicates there are different carrier/firing pin lengths requiring different trigger pin placement to result in the hammer squaring up with the pin when fired.
I suspect although unpublished, there are more than 1 large frame firing pin length to account for the above.

The above is of course secondary to and assuming head space was checked!