Reducing the AI AW Firing pin Diameter ?

[Baldmonk01]

I would like to rebarrel my AI AW to 6.5x47 instead of .260 or 6.5 Creedmoor due to the quality / quantity available brass. Since, there were reports of primer issues I decided to "Reverse Engineer" the problem to figure out what the solution should be.

The AI AW firing pin diameter is Substantially larger than a short action Rem 700 (.308 case head). There is no a debate about it, the AI AW firing pin is "substantially over sized" compared to a Rem 700 firing pin. I have measured both. This is causing primer piercing and primer cratering on small rifle primers using the .308 bolt head. There is also no debate about this, even though people here will tell you otherwise. I ran FE models (I reverse Engineer for a Living)of the different diameters using plastic deformation caused the 2 different firing pin diameter using small primer diameters as the limit of material. The models say the 700 is fine but it should pierce every time using the material modulus of the cup for the AI, but it doesn't so I attribute it to some built in safety factor, or just plain luck. So, I recommend highly against using an un-modified AI AW bolt head for small rifle primers.

So my question is; who can reduce the firing pin diameter of my firing pin and firing pin hole (build up required) of my AI AW bolt down to say the Rem 700 diameter at least? What does this entail (what process)?

I thought I would call GA precision (who I would prefer), but I hear their turn-around is measured in years. So, who else out their does this sort of thing.

 

[MEDICGORDO]

Re: Reducing the AI AW Firing pin Diameter ?

why not just buy a firing pin for the 6.5x47 AE.If they are out yet.

 

[Baldmonk01]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MedicGordo</div><div class="ubbcode-body">why not just buy a firing pin for the 6.5x47 AE.If they are out yet. </div></div>

I am sure that the bolt firing pin hole on the new AE is smaller if the pin is smaller. Otherwise you create an unsupported area around the firing pin. Not something I would like to do.

Plus a new AI bolt head assembly is over $800, just for that one piece.

 

[buffybuster]

Re: Reducing the AI AW Firing pin Diameter ?

The FP hole needs to bushed and a smaller diameter FP fitted. A fairly common procedure with M700's. Shouldn't be too difficult for a AI, as long as the smith is familiar with them.

 

[MEDICGORDO]

Re: Reducing the AI AW Firing pin Diameter ?

i just replied to the post subject,the person i bought my ai/ae mk1 from shot at least 1000 rounds of it out of and never had an issue.

 

[00037]

Re: Reducing the AI AW Firing pin Diameter ?

Have you contacted Stacey @ AINA to get his take on it? Have you contacted GAP to see if they can do it?

 

[Agent Law]

Re: Reducing the AI AW Firing pin Diameter ?

Zak Smith did mention this when he did an article on the 6.5x47mm...

 

[Baldmonk01]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: modifier</div><div class="ubbcode-body">1. Have you contacted Stacey @ AINA to get his take on it?

2. Have you contacted GAP to see if they can do it? </div></div>

1. Yes, on this board but it is hard to get a straight answer out of him (maybe he didn't know what was causing it, so he couldn't). That's why I "Reverse Engineered" the problem to figure out what was actually happening using FE analysis. The AI AW oversized firing pin displaces too much volume (of the available small primer volume)and causes problems. For a simple way of looking at it think of firing pin displacement volume as a function of primer volume.

2. Will call GA Precision this week.

 

[clmayfield]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Baldmonk01</div><div class="ubbcode-body"> There is also no debate about this, even though people here will tell you otherwise.
</div></div>

When there are people on both sides of an argument, isn't that what a debate is?

In the Zak Smith article mentioned above, he pointed out that not only the firing pin diameter but also the firing pin protrusion is different on an AI AW compared to a Remington 700. These things work in concert with each other.

In your model, did you use the same protrusion in both cases? Or was your model based on some sort of pressure based on firing pin diameter and force applied? If so, I imagine that force applied would be less for the case with less protrusion, though it would be tough to determine by how much. That is really going to be based on the characteristics of the spring... which is yet another varying factor between the two actions.

As to the model... it should give the same answer every time right? In real life, I imagine there is a lot of variation in material hardness and thickness plus there has to be a tremendous variation after ignition of temperatures and pressures. Add in differences in headspace of the cartridge causing different amounts of "slamback" and I would expect to see reality be more complex and variable than the model.

 

[Baldmonk01]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Carter Mayfield</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Baldmonk01</div><div class="ubbcode-body"> There is also no debate about this, even though people here will tell you otherwise.
</div></div>

When there are people on both sides of an argument, isn't that what a debate is?

In the Zak Smith article mentioned above, he pointed out that not only the firing pin diameter but also the firing pin protrusion is different on an AI AW compared to a Remington 700. These things work in concert with each other.

1. In your model, did you use the same protrusion in both cases? Or was your model based on some sort of pressure based on firing pin diameter and force applied? If so, I imagine that force applied would be less for the case with less protrusion, though it would be tough to determine by how much. That is really going to be based on the characteristics of the spring... which is yet another varying factor between the two actions.

As to the model... it should give the same answer every time right? In real life, I imagine there is a lot of variation in material hardness and thickness plus there has to be a tremendous variation after ignition of temperatures and pressures. Add in differences in headspace of the cartridge causing different amounts of "slamback" and I would expect to see reality be more complex and variable than the model. </div></div>

1. Yes, I used pin protrusion (measured by depth gauge on used primers). Like I said if you read above, the volume displaced is much greater with the AI AW.

By just using primer volume displaced (pin diameter and protrusion), It already fails terribly. The others don't really affect primer volume that much compared to these 2. If you can fix the firing pin issue, the rest really is negligible.

 

[00037]

Re: Reducing the AI AW Firing pin Diameter ?

Did your model account for differences in firing pin spring weights? The AI spring is massive and undoubtedly puts a lot of force on the primer regardless of pin size.

A smaller pin would increase the pressure and exacerbate any resulting cratering. I'd think it would need a smaller spring to match.

After all, an AI is built to run regardless of the conditions. Everything about it is overbuilt (especially the AW).

Just a thought.

 

[clmayfield]

Re: Reducing the AI AW Firing pin Diameter ?

So how short do you need to make the existing AI AW firing pin to prevent failure? And will it be enough to ignite? Reducing protrusion just seems like a much easier way to go.

 

[BLANKSGUNS]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Baldmonk01</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: modifier</div><div class="ubbcode-body">1. Have you contacted Stacey @ AINA to get his take on it?

2. Have you contacted GAP to see if they can do it? </div></div>

1. Yes, on this board but it is hard to get a straight answer out of him (maybe he didn't know what was causing it, so he couldn't). That's why I "Reverse Engineered" the problem to figure out what was actually happening using FE analysis. The AI AW oversized firing pin displaces too much volume (of the available small primer volume)and causes problems. For a simple way of looking at it think of firing pin displacement volume as a function of primer volume.

2. Will call GA Precision this week. </div></div>

Actually I would say it was a very straight answer but you can't make everyone happy. The simple answer to this is:
1. Small primer, larger firing pin dedicated truly to larger primer such as originally designed a 7.62mm. So it is not optimum by no means.

2. Are we going to offer a smaller firing pin, special bolt head and lower pressure spring for the 6.5x47 Lapua, no not on the planning board.

3. Can the 6.5x47 Lapua be run reliably in the AE or AW series, well that is a potluck answer. Why, lets say we ask 10 different customers which have been running this cartridge for years, 8 of them say good to go, x1 say some issues and x1 writes an article which mentioned possible issues, you come to a conclusion.

4. If direct response to this and others concerns, we discussed the 6.5x47 Lapua, decided between Scott, Dave and myself we would remove and not offer this chambering for direct barrels from AINA to resolve and/or eliminate any concerns or possible issues with the reliability and possible primer issues till further notice. We directly responded as well for all to see, we would and are offering the 6.5 Creedmore which respectively has demonstrated to many to be an overall performer, highly desirable due to cost, availability, large primer ability and many others. That is why we have explained to customers, please do your research, let us know what you would like to see and we will try to assist in the best possible manner we can.

 

[gugubica]

Re: Reducing the AI AW Firing pin Diameter ?

The Process- A smith will turn down the firing pin to a smaller diameter. They will then drill out the bolt head and install a bushing with a hole to match the new pin.

The Problem- I just sent mine to GreTan rifles to have this done. He sent my bolt back with a note that said, Sorry, AIs are to good, the metal of the bolt head is too hard to drill.

So, that leaves us with looking for other solutions...got any ideas?

I thus far just have to make sure my chamber does not get too hot (seems to get worse) and use milspec primers.

Out of curiosity, do people have problems with peircing 223 primers in AIs?

 

[Casey Simpson]

Re: Reducing the AI AW Firing pin Diameter ?

Use CCI 41 primers and a reasonable load and blown primers will probably stop. Medicgordo is right; I never had a blown #41 primer with 123gr's at 2925fpsmv. Nothing is wrong with the firing pin or the hole. It wasn't made for a small primer but if you use #41's you can get away with using small primer rounds like 47L, or run Creedmore or 260 or just quit worrying about it.

 

[gugubica]

Re: Reducing the AI AW Firing pin Diameter ?

I am using #41s and still popping some.

 

[ptd]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gugubica</div><div class="ubbcode-body">
...
The Problem- I just sent mine to GreTan rifles to have this done. He sent my bolt back with a note that said, Sorry, AIs are to good, the metal of the bolt head is too hard to drill.
...
</div></div>

Odd, my brother sent his AE MKI bolt to GreTan many years ago without any issues or notes...

-pd

 

[Baldmonk01]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ptd</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gugubica</div><div class="ubbcode-body">
...
The Problem- I just sent mine to GreTan rifles to have this done. He sent my bolt back with a note that said, Sorry, AIs are to good, the metal of the bolt head is too hard to drill.
...
</div></div>

Odd, my brother sent his AE MKI bolt to GreTan many years ago without any issues or notes...

-pd </div></div>

I just called GreTran myself and they won't do it. Any one else Bushing the firing pin ??

GA Precision told me to call GreTran. I don't know who to call to do the work.

 

[Mag 300]

Re: Reducing the AI AW Firing pin Diameter ?

Call GA and George will take care of it for you

why not stick with 308?

 

[Guest]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MedicGordo</div><div class="ubbcode-body">why not just buy a firing pin for the 6.5x47 AE.If they are out yet. </div></div>

Not gonna happen. There is a thread where Stacey has said(after many calls and emails concerning the primer issue) that AINA will not be offering the 6.5x47 as a standard AE chambering. Call me crazy, but i'm inclined to believe that if there was simple solutions for this using this cartridge, they would probably make it work. It says something to me that they aren't. Just my 2 cents.

 

[Baldmonk01]

Re: Reducing the AI AW Firing pin Diameter ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bill Stoffels</div><div class="ubbcode-body">Call GA and George will take care of it for you



</div></div>

I did they said to call GreTran. Called GreTran and they told me they don't do AI bolts.