Gunsmithing Firing pin bushing thread vs press fit?

[brianf]

Been doing some clicking with all of my extra time.

I see several smiths/companies bushing bolts

seems there are 2 different styles, press fit a bushing that’s a few thousands over

and

Thread the new hole and insert screw/plug


also, some companies go all the way through bolt face compared to just drilling a hole deep enough for the bushing/screw?

Any real differences?

thanks

 

[LRI]

I've pressed and gave up on it years ago. The failure rate was just too high. Shock, awe, etc. . . Things fall out. Least they did for me.

Around 4 to 5 years ago is when we began making our own "plug" and threading it into the bolt face. Not one lick of trouble since then. A lot of shops avoid this mainly because the material hardness does not lend itself to a long and prosperous tap life.

Single pointing it on a lathe is made of bitch so I gotta think that is beyond the reach of most shops using a gap bed engine lathe. I could do it on my Hardinge, but even there it would tend to suck. Very, very tiny, whippy tools.

We ID bore and treadmill using a vertical milling center. It takes all the riff-raff out of the process. Like I said, almost/at half a decade now with this process. Because we make our own threaded inserts we control everything and it's been very successful.

Happy to help.

C.

 

[brianf]

I've pressed and gave up on it years ago. The failure rate was just too high. Shock, awe, etc. . . Things fall out. Least they did for me.

Around 4 to 5 years ago is when we began making our own "plug" and threading it into the bolt face. Not one lick of trouble since then. A lot of shops avoid this mainly because the material hardness does not lend itself to a long and prosperous tap life.

Single pointing it on a lathe is made of bitch so I gotta think that is beyond the reach of most shops using a gap bed engine lathe. I could do it on my Hardinge, but even there it would tend to suck. Very, very tiny, whippy tools.

We ID bore and treadmill using a vertical milling center. It takes all the riff-raff out of the process. Like I said, almost/at half a decade now with this process. Because we make our own threaded inserts we control everything and it's been very successful.

Happy to help.

C.

was hoping you'd chime in, didnt want to tag you

if not pressing, what the need to touch up the face

i noticed on your site that you touch up the bolt face taking a few thousandths

wouldnt you be able to dry fit the threaded plug and make it flush with the rest of the bolt face

do you find the need to set screw the threaded plug or you loctite/epoxy etc

thanks

brian

 

[LRI]

was hoping you'd chime in, didnt want to tag you

if not pressing, what the need to touch up the face

i noticed on your site that you touch up the bolt face taking a few thousandths

wouldnt you be able to dry fit the threaded plug and make it flush with the rest of the bolt face

do you find the need to set screw the threaded plug or you loctite/epoxy etc

thanks

brian

Your "whiskering" the head of the screw to marry up with the existing face of the bolt. When we first went down this rabbit hole we discovered that the bolts don't magically clean up to where the parting line magically goes away. The only way to do that is by peeling a smidge off the face. We also learned that sometimes the bolts aren't as square as one might think. The AI stuff isn't a problem usually, but given that they are almost certainly made in a multi-turret, twin spindle lathe with live tooling, there's no reason to think they wouldn't be "Jonny on the spot." Production bolts have some variances at times. We typically do this in conjunction with a barrel swap so the HS concerns aren't an issue.

For the guns in service, the amount we take has no negative effects. If it did, I'd of heard about it by now as we do a mess of em.

Truth is, a .0015" difference in headspace doesn't amount to one shit of difference as far as the gun is concerned. Whether a person wants to admit it or not, you'll see more than that with your typical chucker press and dies anyway. Brass hardness varies so that means the spring back will vary. Wear on parts, wear on dies, grit under a shell holder, etc...

Look at it for what it is: A .0015" is less than half of the thickness of a sheet of notebook paper. The allowable tolerance for a main bearing on an engine that'll see well north of 100,000 miles is greater than that. I promise your gun won't give two shits.

We fit the threads to where they are a mild interference fit. They are also assembled with locktite. The last thing a person wants is the thing coming loose.

 

[brianf]

Thanks again

 

[Geno C.]

If you fired all your brass, then sent the bolt in to get bushed, all you would have to do is neck size because the headspace increasing .0015” is almost like you bumped the shoulder back that far

 

[FatBoy]

I run anywhere from .002" to .007" HS. FL size every time. I see no difference in brass life or accuracy. Why run them this wide you ask? I have multiple rifle in the same calibers and I don't how good your plumber is, there's going to be differences in HS. A wise old highpower shooter told me early on, loading that case should be like tossing a rat turd into a violin case. At the time I was just neck sizing with a Lee collet ( does a wonderful job) but once you come off the bench and start shooting from position, heavy bolt lift or beating the bolt open due to case head expansion destroys position and causes undue fatigue. Not really relevant to this thread but ..

I haven't had LRI do any of my four bushings as they weren't around for the first two and these were just standard fair Winchesters and one "one off" custom action I had made. If I ever take the plunge and have the balls to have my AI Coopematch done, it'll go to LRI if they'll agree to do the work. Rare beast in the USA, I havent been able to bring myself to modify if.

 

[ken226]

I bushed the firing pin in my SPR 6.5 creedmoor for this reason. I turned the existing firing pin down to .062" and drilled/reamed to bushing to .063" I havn't had a pierced primer since, about 2 years ago, with the same load. I highly recommend bushing the firing pin on these guns.

There's an old thread on it from when I did it. https://www.snipershide.com/shooting/threads/fn-spr-firing-pin-bushing.6907506/#post-7292811

I used a press fit, but in retrospect I should have threaded it. If it ever falls out, I'll thread the replacement.


The FN SPR has a high quality bolt. When milling/drilling, you can tell it's tough steel. I threaded the bolt handle on the SPR, and on a Montana 1999. The difference in steel was pretty surprising.

To contrast, when turning threads on a Montana Rifle Company bolt handle, it was like cutting aluminum, and there was a good size oxy inclusion bubble inside the steel. I'm pretty sure the Montana handle was a casting. Same results drilling the bolt face for the bushing. The difference in steel was surprising.