Firing Pin Bolt Bushing

[Ronin]

This is a project id thought may be benefitial to try on my PGW Coyote.

 

There are a few advantages of using a small diameter firing pin - especially on higher pressure cartriges such as 6.5x47 Lapua and 6.5mm Creedmoor using small rifle primers.

One advantage is a smaller diameter firing pin does not suffer from primer cup flow or cratering, plus more of the case head is supported - it does make a difference.

 

The Coyote action had a large .075" diameter firing pin and a .077" diameter hole.

 

I decided to use a proprietry method to create and fit a bushing, utilising a reamed .065" firing pin hole and turned down the existing pin to .062" extending it in order to allow the pin to run totally encapsulated within the new bushing so there is now zero movement laterally when the pin is released as the trigger sear breaks.

 

A reminder of the Coyote bolt face 

 

I made a bushing from a suitable steel and threaded it

 

 

I also turned down the existing firing pin to the correct dimensions

 

 

Then set up the bolt in a fixture in the lathe (after stripping it down completely) and machined it to accomodate the bushing to an interferance fit

 

 

 

The bushing was then drilled and reamed to the correct diameter hole, then removed and heat treated to similar hardness of the bolt body

 

 

 

The bushing was refitted to the bolt face and bonded in place (belt and braces with interferance fit)

 

Then machined down to existing bolt face surface

 

 

 

 

The bolt removed and reassembled

 

 

Test fired loads:

 

Top row, new firing pin diameter and bushing (37.5g Varget under 123 Scenar)- no cratering and perfectly centred strike

 

Bottom row, old firing pin - (37.5g Varget under 123g Scenar) (cratered primers)

 

 

 

Hppy with this one!

 

 

[Catch-22]

Interesting Andy - I had wondered and asked the question about possibly needing to bush the bolt/firing pin.

Its great to see the before and after - clearly it's made a demonstrateable difference.

I assume you could perform a similar operation for other people who experience similar issues when using small primed brass in a rifle with large firing pin (e.g. Rem700's, Tikka's etc)?? Could be a handy service to offer!

[Ronin]

Cannot do all rifles - Tikkas an issue with the pin being pressed into the sear..though im sure the pin could be turned down in another manner or held in collet.

Remington and clones would be a relatively simple task, though rivetted extractor / standard extractor may need replacing as they are often damaged when stripping them out

 

 

[chaz]

British/English engineering/Gun-Smith craftsmanship at it's best. You can't beat it! 

Thanks for sharing Ronin.

[Re-Pete]

What about a Savage mod 12? We've had the same problem since re-barrelling it in 6.5x47. The bolt head is removable, but has the two lugs so I guess it would be difficult if not impossible to centre accurately.

Re-Pete

 

[Ronin]

The removable head of the savage would be relatively easy to centralise.

 

Not sure about the head depth for the method I’ve used but I know of riflemiths in the states using a simple pressed in bush in this type of rifle. Then machining down the pin to the correct diameter

 

i can’t say if one could encapsulate the pin at the bolt head either without examining one.

 

I haven’t any savages with me at present.

[dully1963]

Hi just wondering would you have to send the full gun for proof as they can not proof just the bolt by itself ?

[Ronin]

Not possible to carry out a proof test without firing two proof rounds in the chamber of te weapon tested.

 

Bit of an issue if the bolt is sent on its own - hence why the complete weapon has to be submitted 

[johnnyb0_1]

Would this translate to an Accuracy Int. AW or an AX?  How about Sako TRG 22, 42?

I drive them hard.  Interesting and informative post, thanks.  JP.  

[Ronin]

I am about to try machining a sacrificial (scrap) Ai bolt and see how well that goes 

One of the rifle smiths in the states who is very well known (Thomas Gonzales) has successfully bushed an Ai bolt but said it was difficult due to their hardness.

Will see how I go on and post results here 

 

May be a few days though as I have other work to get on with 

 

 

 

[palo]

Good you give me a rough idea of a price to do this conversion on my Remington 204.

You can pm me if you prefer. 

[johnnyb0_1]

Cheers Ronin, Please keep posting yours vids.   all very interesting.  JP.

[baldie]

Without wanting to party poop. The mention of AI's will always provoke the factory response.

Having just had to sort out an AXMC , That had both its bolts badly bushed, and ruined, its a very expensive mistake to rectify.

The factory will NOT guarantee any rifle, that has had its bolt head, messed with in such a way. The engineers there where absolutely aghast at what had been done.

There is no need now, the small firing pin bolt head in .308 BF and .338 is available.

[Scotch_egg]

How much are the new bolts Dave?

[Ronin]

Thanks for that Dave

 

I wouldn’t expect any manufacturer to uphold a warranty on a part that had been altered from original spec by a third party.

 

Id like to clarify that the method I have used is the same used by industry acclaimed accuracy smiths and custom action manufacturers in the US as the way to go to rectify the issue with oversize firing pin and bolt firing pin holes (without the expense of purchasing a new bolt and firing pin) 

 

It’s the same method that has been used to remove pitting and wear on bolt heads and action faces on firearms for decades.

 

I have no idea what was done to the two AX MC bolts to which you refer,  but they must have been machined out too far or without sufficient supporting shoulder (etc) or had bushing material of inapropriate strength  / hardness re-inserted to cause such concern with the engineers at AI

 

There is documented case study on another US rifle smiths web page about carrying out the very same alteration to an AI bolt and firing pin - do you know if  there were similar concerns from the factory about this work being undertaken ,,?

 

The thread was started to show what I had done to resolve the issues I’d found with my own PGWDTI Coyote.

Within the post I pondered if the same method could be used to resolve the same known issues with other bolt heads (including AI) and as I have a scrap bolt here, I intend to investigate that method to resolve that - as an experiment. 

 

 

 

 

 

[trucraft]

Lovely Job. 

A joy to see how things should be done. 

[lapua]

how did you mange to get a scrap AI bolt?

 

[Ronin]

Bought with a load of other spares for other manufacturers from a fellow RFD 

[baldie]

The problem with the bolts Andy, was that although the bushes had been made quite nicely, the firing pin hole was not central, on either bolt.

This rapidly bent the [ Weakened] firing pin tip, which looked like it had been ground down on a bench grinder.

As you say, its an age old fix in the states, and I know, done correctly...works, and is safe.

Yours looks a lovely job. Personally, I would silver solder the bush. That would then mean re hardening the bolt head, but a remmy, or other factory head, are not that hard anyway.

I suppose this is the bit that worries me a little.

Just playing devils advocate, I see it as introducing a possibly non type of steel, into an unknown type/hardness. Probably no problem at all on a remmy etc.

The AI bolt head though, is a different kettle of fish.

I watched them being EDM'd at the factory. Cant remember the steel grade, but it wasn't run of the mill. They are then heat treated. Known to be as hard as woodpecker lips.

Current models have the small pin/hole. The factory did this to help with the cratering problems on small primered cases, even though, they don't produce calibres using them. The problem never arose until people started putting 6.5 x 47 etc onto the guns.

It isn't a problem on all. It can usually be alleviated by altering the protrusion [within factory tolerances ] even on the old AW.

The problem on all doesn't just stem from the pin/hole. Many factors can compound this.

Case wall grip, plus or minus.

Bore dimensions, etc.

I've built a lot of 6.5 x 47's on remmy's with no such problems, and a couple that did crater.

Personally, i've never worried about cratering. If the primer doesn't pierce at the velocity you require, the job is good. A cratered primer isn't going to be re used....it just looks ugly...like an ugly wife/car/dag.?

A good tip is to use a BR/mag primer. That helps a lot. If that isn't quite it, try the remmy 7.5 s/r primer...they are like bell metal, and seem to work just the same as a br4.

Dave, the bolt head can be replaced. Its a factory re fit, and the gun is required, and will be re proofed. If you are interested, I can enquire of the costs.

[Ronin]

Cheers Dave 

 

I wondered about the heat treatment / hardness issue and on my own bolt and used a hardened insert of suitable grade steel.

Thats the good thing about AI that the firing pin protrusion can be altered to avoid this issue.

 

Have to say I didn’t encounter it on the AW and AX I owned and re barrelled several times to 6.5/47. Neither rifle suffered from cratered primers and neither suffered with accuracy. In fact my old AW was the one used by Darryl to attain factory benchrest champion when he first started shooting the discipline.

The PGW did have cratered primers at mild loads - hence my reason for researching and carrying out the alteration as I would like to run it slightly faster using slightly heavier bullets and didn’t want to cause unecessary wear on the firing pin being dragged out of the primer cups,,,,

Bore diameter of the barrel is not overnight (Bartlein) and chamber is cut to a few tenths run out so those factors are not the issue.

The bolt of the PGW is one piece machined and heat treated - like AI

I can understand why the factory techs raised eyebrows at a uncentered firing pin hole - should not have left the place of whoever did the “work”

I think, to avoid any controversy I will leave looking at the AI bolt to a “rainy day project” and not post any more on the subject. ?

 

 

 

 

 

 

 

 

 

[lapua]

38 minutes ago, Ronin said:

Bought with a load of other spares for other manufacturers from a fellow RFD 

I wonder how the bolt became spare, you would have thought it would have stayed with its action. Its not like they ever  blow up or anything..

[Ronin]

No idea

It’s scrap - damaged.

 

 

 

 

 

 

 

[bradders]

Interesting thread

it’s also interesting to note that while Baldie says Remington bolts are soft and Acccuracy bolt “heads” are hard as nails....both are in Military service and have seen countless actions, while literally millions of Remingtons have been made and many are in service with designations such as M24 and M40 etc, those “soft” bolts don’t seem to stretch or compress and have headspace issues, while Andy does have a hardened AW bolt head that is scrap.....it leads me to wonder, how hard does a bolt need to be?

Remington, and others have never deemed it necessary to make a separate bolt head system, so I wonder what’s the true mileage in having one?

 

[baldie]

I suppose it depends on what its intended use is Mark. Its also a simple job to fit a new one, in conjunction with a breech ring, and the gun will go on to do many more years of service. I'm re fitting some fairly old AW's these days, the rifle can have literally any part serviced/updated, meaning it never need go out of service.

A customer accidentally overloaded a .338 AW with the wrong powder. The bolt welded itself to the breech ring.

The factory [ on the load data ] worked out that the round produced over 130, 000 pSI.....over twice the safe working pressure.

The action was x rayed, and found to be sound. The bolt body was sound. The bolt head and breech ring were replaced and the gun was fine.

As the engineer said  " a rifle from anyone else, would have blown their head off"

I think he was quite correct.

most bolts are actually 2 or 3 piece, including remingtons. The bolt head is brazed into the bolt shaft, and machined.

i saw a Lawton a while back, where the bolt head had actually gone on that joint, which was a first for me.

[Scotch_egg]

Baldie,  Thank you for offering to get me a cost for the new bolt. For now I will see how I’m getting on. 

Although my AT was a factory 6.5X47, it begs the question that by offering a smaller firing pin on current rifles was the large firing pin not fit for purpose on the factory 6.5X47. 

I don’t want to detract any further from Ronin’s topic so probably don’t answer that question. 

What I will say is the job Ronin has done looks smart and can fulll well see that it would give the piece of mind there is one less thing that would affect accuracy. Whether it does or doesn’t matters not. If it’s in your head it will affect you.