Is my rifle's chamber too short?

[hkfan45]

I recently received a custom rifle built by Pierce chambered in 308. The rifle was chambered using a Palma Bisley match 308 chamber. I plan to shoot 168 and 175 SMKs, 168 Berger hybrids, and 155 scenars and SMKs. When using the stoney point OAL guage with a 175 SMK dummy round, I get an OAL of 2.805 when touching the lands. Does this sound right? Was this chambered correctly?

While I plan to handload, I would like to be able to shoot factory match ammo every so often. Since most factory ammo is seated to 2.800 (FGMM), is my rifle's chamber too short to safely shoot this ammo? Will the throat grow over time and allow me to eventually shoot this factory ammo?

 

[6brshooter]

Yes the throat will erode over time, since it is 308 instead of a hot 6mm it will be longer before the throat moves. If u are set to reload now then the factory rds can have the bullets bumped back to 20 thousands off or whatever u want. Not sure how crimped factory would be, best to avoid that stuff. I remember reading here or at 6 mmbr.com that bumping the bullets back in 118lr showed better es/sd, something about the sealant used on the bullet/case caused erratic es. Bumping back broke the sealant.

 

[buffybuster]

Looks about right. Shoot is and see how it does. Bet it's shooter.

 

[hkfan45]

would the 175 FGMM be safe to shoot? I've checked and the base to ogive of the factory ammo is only about .005 shorter than my chamber using the 175 SMK dummy round. The FGMM 175 chambers fine, but it's probably kissing the lands. Would I have serious pressure issues?

 

[bigedp51]

You could jam your bullets and as long as you work up your load you will fine. A old fire forming method is to jam the bullet hard into the rifling to hold the base of the case against the bolt face. Just remember normally when your bullet is "off" the lands the pressure builds enough to get the bullet moving then it hits the lands and the pressure builds even higher.

Just seating your bullet deeper into the case also raises the chamber pressure, and my .223 bolt action has a longer throat than my 5.56 AR15 rifles do. At AccurateShooter.com many competitive shooters shoot loads that are jammed into the rifling and as long as you start low and work up your load you will be fine.

You might be surprised, I was fire forming some .243 cases jamming the bullets and fired the best group I have ever shot in 46 years of reloading by accident. The old single shot schuetzen rifles would push the lead bullets into the throat using a false chamber and pre-engrave the bullets into the rifling. They would remove the false chamber and load a charged case w/o a bullet with a hard paper disk holding the powder in the case. These schuetzen rifles shot groups that rival many competitive rifles today.

Now ask yourself how much "jump" does a muzzle loader bullet have?

Below Clymer chamber and free bore lengths.

 

[former naval person]

Each of those bullets you mention have a slightly different ogive, so touching the lands will vary with the bullet. FGMM isn't loaded to peak pressures so you'll be okay.

 

[hkfan45]

Looking back at the Bisley reamer print for my chamber, it looks like the old version with .080 FB was used, rather than the newer version of the reamer with .088 FB. Could this be the issue? Can anyone comment on this?

 

[DanSavage]

I've got a factory Savage 24" .308 varmint barrel off my 10FP that is currently sitting on the shelf but I remember that it measures around 2.800 with the 175SMK. I wouldn't recommend this because I think it's under the book value, but I worked back to 2.780 coal and it shot really good with 44gr Varget and a Winchester case. It was slightly compressed and shot 2650 feet per second at 8" from the muzzle. I have other great loads for the barrel including jammed recipes. I took it off because it copper fouls really bad and takes forever to clean, even after the 1,500 rounds it has through it, but it was always accurate and easy to find a good load with the short throat.

Break it in and check again.

 

[bigedp51]

I've got a factory Savage 24" .308 varmint barrel off my 10FP that is currently sitting on the shelf but I remember that it measures around 2.800 with the 175SMK. I wouldn't recommend this because I think it's under the book value, but I worked back to 2.780 coal and it shot really good with 44gr Varget and a Winchester case. It was slightly compressed and shot 2650 feet per second at 8" from the muzzle. I have other great loads for the barrel including jammed recipes. I took it off because it copper fouls really bad and takes forever to clean, even after the 1,500 rounds it has through it, but it was always accurate and easy to find a good load with the short throat.

Break it in and check again.

DanSavage, sorry they don't have these little Devils here so I borrowed one.

New Savage button rifled barrel bore scope photos.

Throat

One inch from the muzzle.

And why they invented foam bore cleaner.

Custom made, hand lapped barrel.

Sorry DanSavage, The Devil made me do it.

(I have two Savage rifles with stock barrels and lots of foam bore cleaner)

 

[awp762]

If your measurements are correct you have .005" clearance from the ogive of the factory ammo to the lands. In my opinion it is enough of a jump to use the factory ammo. I normally load .002" from the lands which means due to bullet variance some of my loads touch the lands based upon 450- 175 smk's I measured base to ogive. I did this for curiosity's sake, yes all one lot. I don't have pressure issues. The OAL of my loads vary due to the variance in the SMK's I just loaded. I pulled 2 of them to take OAL measurements after seeing this post & they are 2.821" & 2.804" but the base to the ogive on both is 2.153" - 2.1535" which is where I set it at to give me .002" jump. I never use OAL except to make sure my loads fit into the AICS magazine.

Pierce Built several rifles & chambered several barrels for me, all of them hammer.

You can always use an old school method of checking the jam, use a match and blacken your bullet tip, chamber it & see if any of the black is removed.
You have the stoney point tool so save yourself a little bit of hassle & get a Sinclair bump & comparator inserts. Didn't see anything showing you have this.

Go shoot that thing & report back.