Using Large Firing Pin with 6.5 Creedmoor SRP

[Konocti's Wigwam]

I've searched and found a couple threads that briefly discussed this, but wanted to run my current plan by others that might know more about this.

I have a PTG bolt with a large firing pin. When I bought it there was no small primers for 6.5 Creedmoor.

Recently I learned I could use the large firing pin with small primers, but in doing so there could be high pressure on the brass pocket.

First, what do you think about using the large firing pin with small primers? I plan to use Lapua brass.

Second, do you think using either Military and/or AR thicker primers would withstand possible higher pressure better?

Spoiler Alert: I have more AR Small Rifle Match than I do regular Small Rifle Match, buy wanting to understand if pressure will be an issue or not in this configuration?

 

[BoydAllen]

This is total non-issue. Most rifles have what you refer to as a large firing pin. If you change a component in a load, you should do some testing both for tune, and for pressure. This would involve lowering the powder charge and working back up. Back in the day a friend had loads for a couple of Ackley Improved varmint calibers that were apparently right at the ragged edge on pressure (AIs do not show pressure as clearly as the non improved versions.) A change in primers caused primers to be blown out of cases. If he had dropped back a couple of grains and done new workups, that would hot have happened. Do your own testing. Different rifles can produce significantly different pressures with the same load.

 

[JOE360]

I have a 70's rem 700 that is a 6.5 creed now. With larger firing pin. If i use cc450 small primers i get primer pericing at book max loads. The same load with large primers look like zero pressure. I believe this is common in many guns. Lapua makes large primer brass now which is great.

 

[Leeman]

If you're planning on running max pressure loads with the SRP you may have to get the bolt faced bushed and pin turned down otherwise you may get primer cratering and blanking, depending how much clearance the pin has in the bolt face. It's no big deal getting that done. Otherwise just stick with LRP brass or as Boyd says just work up the load with SRP brass to where the pressure signs on the primer are acceptable to you.

 

[Konocti's Wigwam]

This would involve lowering the powder charge and working back up.

I wouldn't shoot them without working my load out, but thanks for mentioning that.

I was planning to use the large firing pin with small primers, but in reading what you say I think I should stick with the large primers possibly. I have 100 pieces of Norma large primer brass, and although I ordered 100 pieces of small primer from a guy here, I could sell them most likely and look for Lapua with large primers.

Could I just turn down the end of the firing pin? Seems as long as only the end is turned down smaller, it would still be held fine for the motion of the firing pin.

@JOE360 Do you think the CCI 41 would exhibit the same pressure with a large firing pin? Sounds like you only checked with the 450s which are the thinner ones.

Both the GM205MAR and CCI No. 41 are supposed to prevent the light strikes, but I'm not sure about pressure. Might be good to stay with large primers, but I'd like to understand this better. I will need to work a load up and inspect them on this build for myself. Obviously it's not something you can decide for my rifle, which is not even built yet!

Currently I have 100 large primer and 100 coming with small primer. I have plenty of primers. I will just keep the 200 pieces I have until I figure out if I will ultimately go small or large primer.

 

[JOE360]

I wouldn't shoot them without working my load out, but thanks for mentioning that.

I was planning to use the large firing pin with small primers, but in reading what you say I think I should stick with the large primers possibly. I have 100 pieces of Norma large primer brass, and although I ordered 100 pieces of small primer from a guy here, I could sell them most likely and look for Lapua with large primers.

Could I just turn down the end of the firing pin? Seems as long as only the end is turned down smaller, it would still be held fine for the motion of the firing pin.

@JOE360 Do you think the CCI 41 would exhibit the same pressure with a large firing pin? Sounds like you only checked with the 450s which are the thinner ones.

Both the GM205MAR and CCI No. 41 are supposed to prevent the light strikes, but I'm not sure about pressure. Might be good to stay with large primers, but I'd like to understand this better. I will need to work a load up and inspect them on this build for myself. Obviously it's not something you can decide for my rifle, which is not even built yet!

Currently I have 100 large primer and 100 coming with small primer. I have plenty of primers. I will just keep the 200 pieces I have until I figure out if I will ultimately go small or large primer.

Based on how the 450's worked i cant imagine the 41 primers solving the issue i was having. And i really don't thing grinding the pin is will work or is a good idea.

 

[lazyMlazyK]

@JOE360 Do you think the CCI 41 would exhibit the same pressure with a large firing pin? Sounds like you only checked with the 450s which are the thinner ones....

The 450s are on the thick end of the spectrum. I'm not sure on the cup thickness of the CCI 41 though.

 

[BoydAllen]

I wouldn't shoot them without working my load out, but thanks for mentioning that.

I was planning to use the large firing pin with small primers, but in reading what you say I think I should stick with the large primers possibly. I have 100 pieces of Norma large primer brass, and although I ordered 100 pieces of small primer from a guy here, I could sell them most likely and look for Lapua with large primers.

Could I just turn down the end of the firing pin? Seems as long as only the end is turned down smaller, it would still be held fine for the motion of the firing pin.

@JOE360 Do you think the CCI 41 would exhibit the same pressure with a large firing pin? Sounds like you only checked with the 450s which are the thinner ones.

Both the GM205MAR and CCI No. 41 are supposed to prevent the light strikes, but I'm not sure about pressure. Might be good to stay with large primers, but I'd like to understand this better. I will need to work a load up and inspect them on this build for myself. Obviously it's not something you can decide for my rifle, which is not even built yet!

Currently I have 100 large primer and 100 coming with small primer. I have plenty of primers. I will just keep the 200 pieces I have until I figure out if I will ultimately go small or large primer.

I suggest you reread my first sentence. The main reason most shooters go to a smaller pin tip is that thier pin pin tip has too much clearance. If you are not having problems related to that I would leave lt alone.

 

[WSnyder]

You are way overthinking what you've read on the internet. Think about how many millions of Rem 700's that are out there with the original large firing pin tip that were chambered for cartridges with small primers????? How about the many early BR actions that are out there with large pin tips shooting very high pressure with the PPC's and small primers????

Total non issue, follow Boyd's advice and properly work up your load for that combination.

 

[Konocti's Wigwam]

I suggest you reread my first sentence. The main reason most shooters go to a smaller pin tip is that thier pin pin tip has too much clearance. If you are not having problems related to that I would leave lt alone.

You are way overthinking what you've read on the internet.
...
Total non issue, follow Boyd's advice and properly work up your load for that combination.

Thanks to both of you, @WSnyder you are 100% correct, I AM overthinking this, but wanted to make sure I don't have a problem. I don't need no stinkin' anything coming back towards the shooter.

I will work out and test both to see if any pressure signs exist. I'm pretty anal about that type of stuff, safety is always first on my list.

You guys have made me feel much more comfortable...I will do proper load testing when I get to that point.

 

[Old Navy]

I suggest you reread my first sentence. The main reason most shooters go to a smaller pin tip is that thier pin pin tip has too much clearance. If you are not having problems related to that I would leave lt alone.

Exactly!

 

[Konocti's Wigwam]

I suggest you reread my first sentence. The main reason most shooters go to a smaller pin tip is that thier pin pin tip has too much clearance. If you are not having problems related to that I would leave lt alone.

Boyd,

When you say the tip has too much clearance, do you mean the hole through the bolt face?

I don't plan to do anything unless I do have a problem, but was originally asking because I didn't understand large vs small firing pin.

However, wouldn't the thicker primers be able to withstand more pressure in most cases? Or is that primarily having to do with being able to prevent the light strikes?

Alan

 

[Bill K]

You are making a mountain out of a mole hill. Don't be the least concerned about large/small firing pins.
Most are on the large size really, if you did some measuring. But that is a waste of time.
Your firing pins will do the job and work with either small or large primers.

 

[BoydAllen]

Boyd,

When you say the tip has too much clearance, do you mean the hole through the bolt face?

I don't plan to do anything unless I do have a problem, but was originally asking because I didn't understand large vs small firing pin.

However, wouldn't the thicker primers be able to withstand more pressure in most cases? Or is that primarily having to do with being able to prevent the light strikes?

Alan

The OD of the pin tip having too much clearance within the I d of the hole in the bolt face…We shoot 205s at very high pressures using all tip diameters. Yes thicker will take more pressure, but there are other factors involved.

 

[Konocti's Wigwam]

The OD of the pin tip having too much clearance within the I d of the hole in the bolt face…We shoot 205s at very high pressures using all tip diameters. Yes thicker will take more pressure, but there are other factors involved.

Now that makes sense. You're teaching me something here. My hopefully final question to this thread.

As the firing pin gets hammered into the primer, does this mean that over time that OD of the firing pin wears and eventually looses part of the OD that abrades as it pushes through the bolt face? I would just like to understand, is this a condition of wear?

I would think that when a bolt is created new the firing pin fits close to if not perfect. I would also hope that some of the better bolt makers use better materials these days, which could also be why you say don't worry about it if there's no signs of pressure???

Thanks for taking the time to explain that to me. Bolts are new to me.

Alan

 

[BoydAllen]

It is a matter of tolerances held (or not) when the bolt was made. Typically, custom actions do not have this issue. This does not have to be perfect, but when it is beyond a certain point there can be problems.

 

[Konocti's Wigwam]

It is a matter of tolerances held (or not) when the bolt was made. Typically, custom actions do not have this issue. This does not have to be perfect, but when it is beyond a certain point there can be problems.

I guess that kinda makes sense. My bolt is is about .0010"-.0015" smaller, so I think it will be a good fit. PTG made the bolt for me a few years ago. I bought the PTG bolt knowing that the PTG reamer and Redding dies all use the same dimensions. Maybe that was a misunderstanding on my part, but for better or worse that is what I have now. PTG is making me a 2nd bolt for the 2nd rifle, and it's about 6 weeks out.

Like everything about firearms, each rifle really needs to be looked at on a case by case basis. (hey, a brass pun for 'ya there! )

 

[msalm]

It’s only an issue if you get blanking on your primers. This IS a thing with a larger fp diameter and srp’s. If you blank primers, you need to bush the bf and turn down the fp tip. If not, no worries. It’s a crapshoot if you’ll have that problem or not. I had a 6.5x47 Lapua that blanked even mild loads on a Rem 700 action. Bushed it and problem solved. It’s not so much clearance of the fp either, it’s the radius of the tip that under pressure retracts below the bf and creates a cookie cutter effect where your primer material shears off around the hole. Win 70’s are especially poor at this with fp’s that measure over 80 thou (.085+”). I did a 6x47 Lapua on one of those and blanked every single round with starting loads. Bushed the bf to .070” and turned down the bf problem disappeared.