Firing pin measurment

[Mopardoctor]

I decided to order a bolt and firing pin from Alexander Arms. I figure AA should have better control over the bolt tolerances than any aftermarket manufacturer. It will also make my Grendel happier knowing that its bolt is from it's creator.

Mopar Doctor

[NugginFutz]

I'd checked all four of my bolts, which came from various sources. In no particular order.

Manufacturer	Bolt Length	Depth	Bolt Lug
Tactical Ammunition 1	2.809"	0.136"	0.284"
Les Baer Custom	2.810"	0.135"	0.280"
Larue Tactical	2.810"	0.135"	0.281"
Millennium Manufacturing 2	2.810"	0.136"	0.286"

¹ Seriously - their website is now officially beyond help.

² Monster Group Buy


In all cases, firing pins are completely interchangeable (right?) and bolts head space identically between all rifles (again, right?)

When at the range or in the field, a second rifle is always the perfect backup. Plus, there is tremendous peace of mind when cleaning BCG's with no need to concern myself about accidental mixups.

[Mopardoctor]

Got my AA bolt and AA firing pin and pin protrusion is now .028". I also found that Hornady primer pockets are shallow .001 - .002" . Cleaned up the primer pockets with a KM primer pocket correction tool.

Mopar Doctor

[TraderRik]

Anyone know where to buy a correct firing pin for a Toolcraft nitride Grendel BCG? I would like to have a spare. I have searched online and looked at all my usual sources and find nothing that specifically states a particular pin will work. In fact, most sites I've gone to don't even sell Toolcraft pins separately.

Thanks!

[VASCAR2]

I have looked for a source for Odin Works, Brownell’s or Toolcraft 6.5 Grendel firing pins with no luck. To my knowledge they were the only companies using a 2.80 length bolt. I read where one forum member posted the length of a LaRue 6.5 Grendel bolt at 2.80 but then a few months later another forum member posted the length of his Larue 6.5 Grendel bolt a 2.810. With manufacturing tolerance and vendors changing sources I don’t know which bolt LaRue is currently shipping.

If I needed a shorter firing pin I would order a Stainless Steel AR-15 firing pin. I would check the firing pin protrusion and if it was excessive I’d shorten the firing pin to be within spec. I wouldn’t want to shorten a chrome plated firing pin as you might remove all the chrome from the tip. Same with a Nitride firing pin, shortening probably would get into the softer steel underneath the Nitride surface.

Firing pin protrusion spec is minimum .028 to maximum .036.


Here is a link to a SS firing pin which are available from several vendors.

https://www.midwayusa.com/product/1003307442/colt-firing-pin-ar-15-stainless-steel

[VASCAR2]

The milspec length for a AR-15 firing pin is 3.280 plus or minus .001. Probably need to shorten a firing pin to 3.27 with a 2.80 length 6.5 Grendel bolt. I think it still best to measure the bolt, firing pin and protrusion before shortening a firing pin. I’d probably use a file to shorten a firing pin.

[grayfox]

Toolcraft.com is their website I think...

maybe give them a call.

Toolcraft, Inc.
1877 Rutherford Road
Marion, NC 28752
Phone: (828) 659-7379
Fax: (828) 659-7329

[TraderRik]

Thank you both!

[c3k]

I think someone mentioned shortening the firing pin at the primer end? I'd think (as a total newb), it'd be best to leave the tip nicely radiused and to file down the back of the pin where the hammer strikes it. Just my .02.

[Lastrites]

I think someone mentioned shortening the firing pin at the primer end? I'd think (as a total newb), it'd be best to leave the tip nicely radiused and to file down the back of the pin where the hammer strikes it. Just my .02.

Unfortunately reducing the back of pin will do nothing for shortening the tip protrusion, easy enough to find a stainless steel FP and circumcise the tip a bit for the reduction. Go slow and measure often or compare to one that is of the shorter length if you currently have one.

[VASCAR2]

I bought a PSA 12” Nitride 6.5 Grendel pistol kit. Got it together Friday and shot it Friday and Saturday. Functions 100% and firing pin indentations look spot on. I decided to measure the bolts and firing pins of various firearms to see how much difference there is.

PSA 12” Nitride barrel, Nitride 6.5 Grendel BCG

Bolt length 2.808

Firing Pin length 3.275

Faxon 18” build PSA Nitride BCG Monster GB bolt

Bolt length 2.812

Firing Pin length 3.2765

Faxon 16” Build Precision Firearms Nitride BCG

Bolt length. 2.8095

Firing Pin length. 3.277

Shilen 20” build Shilen supplied bolt PSA Phosphate Prem. BCG

Bolt length 2.814

Firing Pin length 3.275

J&T Distributing upper (AA bolt) 6.5 Grendel upper

Bolt length 2.814

Firing Pin length 3.274

I also measured my 5.56/223 AR-15 bolts and firing pins

PSA 16” SS midlength Freedom

Bolt length 2.798

Firing Pin length 3.2755

RRA Build RRA BCG

Bolt length 2.7965

Firing Pin 3.279

Colt 20” Competition H-Bar

Bolt length 2.799

Firing Pin length 3.280

After looking at these different measurements I think in a mass produced industry an employee assembles a bolt carrier group from bins of parts. I suspect a gauge is used to verify the firing pin protrusion is between .028 and .036. If the firing pin protrusion is out of spec they might try a different firing pin bolt combination. If the parts fail they go in a reject bin. There is a .008 variation to account for different length firing pins or bolts. Tolerance stack and you can get excessive or inadequate firing pin protrusion.

[VASCAR2]

Here is a composite list which makes comparisons easier.

Firing pin lengths

3.275
3.2765
3.277
3.275
3.274
3.2755
3.279
3.280

Shortest 3.274
Longest 3.280
All within .008

Bolts 6.5 Grendel

2.808
2.812
2.8095
2.814
2.814

Bolts 5.56/223

2.798
2.7965
2.799