Short throat in custom rifle

[Hoosier]

I purchased a rifle from a friend that he had custom built. It's a Remington action with a Pac-Nor barrel. The rifle is chambered for 7mm WSM. In the note provided by the gunsmith, he states the rifle has a short throat. I have never encountered a "short throated" rifle. I hand load most of my ammo, but due to the shortage of reloading components, I purchased some factory ammunition. Of course, it will not chamber in the rifle.
I would like to learn the advantage of the short throat and possible recommendations for creating handloads. I understand the pressures would be higher due to the projectiles pushed in to the riflings.
Any guidance would be appreciated.
Hoosier

 

[Cort]

I would not shoot the factory stuff until I learned why a factory round will not chamber. I recommend that you take one factory cartridge a part and confirm that the empty case will chamber. If the factory case will not chamber, then your chamber does not meet SAAMI headspace values. You have to decide what to do about that; either have the chamber recut or stick with handloaded rounds tailored to that particular chamber.

If the factory case chambers, then the only issue is the throat. How much jam does a factory cartridge have? More than 10 or 15 thousands is greater than I would be comfortable shooting. Re-seating the factory bullet to allow chambering is more than I would do also. I would probably pull all of the bullets, reload the cases with a starting load of known powder and reseat the bullets at a depth that works.

The short throat initially allows you to shoot shorter bullets and seat them close to the lands. As the throat erodes, you can chase the lands by seating the bullets out further and/or using longer bullets. Consequently, useful barrel life is extended.

Good luck with your new purchase,

Cort

 

[X Ring Accuracy]

FWIW, jambing a round does not create high pressure. Your best bet is to read up on reloading and how to find the lands to set your seater die to. You may find its a real shooter.

 

[Hoosier]

Thanks Guys...The gunsmith sent a empty case with the rifle. The note that accompanies the rifle speaks of firing a couple hundred rounds, and then the throat should be able to allow longer projectiles. Also, it was my first thought to pull the projectiles of the factory loads, and work up a load for the rifle. I usually fire heavier/longer projectiles in my rifles, but I was concerned about OAL for this one. I will most likely begin with lighter projectiles. I have the Hornady cartridge gauge for this one, so I better check the throat. I didn't know the pressure would not be an issue with the projectile jammed.
Thanks again,
Hoosier

 

[taxman]

You did not mention if the chamber has a tight neck or not? If it is a tight neck, factory ammunition will not chamber. As a factory loaded round may have a greater diameter than the neck if a custom chambering was used. A quick call to the gun smith is cheap insurance, just a thought!

 

[Cort]

Jamming can definitely alter pressure. Pressure is related to volume and temperature both. When a bullet jumps at ignition, the volume in the case grows as a result of the bullet entering the lands whereas when it doesn't move, the volume is fixed until enough pressure builds up to overcome the friction of the lands. Depending on the pressure curve created by the powder, the pressure can go dangerously high when the volume fails to increase due to the lack of jump. One should always reduce the load when jamming a bullet until the pressure in the cartridge is understood.

Err on the side of caution is the best advice that I can offer.

Cort

 

[Hoosier]

Thanks all....I appreciate all the feedback.
Hoosier

 

[Hoosier]

I spoke with the gunsmith...he said the chamber and throat was made with a tactical rifle reamer. The chamber and short throat is meant to be tight to increase accuracy. Factory ammunition can be fired after seating the projectiles deeper with an adjusted seating die. Case necks do not require turning or any adjustment.
Thanks all that have addressed this thread.
Hoosier

 

[turbo54]

I don't think someone can accurately predict the ammo will be safe provided you simply seat the bullets deeper.

The factory ammo is tested and found to be in-spec "AS-IS"... No promises if you modify it!

If we were talking about .005", I wouldn't even bring it up, but if you can't chamber a cartridge because the bullet is so jammed, that is an appreciable amount of "jam".

I'm curious how far you'll have to seat the bullets to allow chambering.

 

[Hoosier]

I was able to chamber the factory ammunition this evening. The bolt locks up pretty tight. When I extract the cartridge there isn't any mark on the projectile. I believe that would indicate it's touching the lands, but not jammed tight enough to mark the projectile. My first attempts at chambering a factory rounds was not to force the bolt closing, but after talking with the gunsmith, I added some extra force. The gunsmith told me a cartridge would be tighter than normal, but if it measured 2.8 it would close. He instructed that the chamber being a tactical one, it would take more force than normal to close the bolt. I am new at have a short chamber, so I was reluctant to add the force required.
The gunsmith assures me with practice the rifle would have exceptional accuracy. The Pac-Nor barrel is a super match, the action has been trued, and the trigger is at 2.75 lbs. without any creep. The barrel bead blasted, the action has be pillared bedded and glass bedding added. If I can learn to post pictures I will add one to this thread.
Hoosier.

 

[SinMan]

It might just be me but it bothers me that he keeps calling it a "tactical" chamber. Is it a short freebore, is it a tight neck? Don't call something tactical to make it sound awesome, say exactly what it is. If you aren't marking the bullet its not the freebore. Sounds to me like it has a tight neck and that could give you pressure problems. Did you ask to have a special chamber? Did he just elect to cut it with his cool guy reamer? If you want to shoot factory ammo and most hand loads I would most likely cut it with a standard reamer.

 

[turbo54]

I agree with the above.

Until you identify exactly what is causing the stiff bolt closure, I don't think you should fire it.

Is the headspace set so short you're actually "crushing" the cartridge into the chamber?

Is the chamber's neck small, such that you're actually "pressing" the caseneck in there?

Are the body dimensions of the chamber so small and tight you're "pressing" the cartridge into the chamber?

Is the throat so short you're jamming the bullets into it?

Your stiff bolt could be caused by any of these reasons, and to be quite frank, none of them are good when we're talking about FACTORY AMMO....

Because:

1. If you measure the "headspace length" of factory ammo, it is always several .001"s under SAAMI-spec'd minimum chamber headspace. If factory ammo won't fit, the chamber is wrong, and is too short.

2. If the chamber's neck is too small for factory ammo, and therefore required neckturning, it is not a "tactical" type chamber, and the barrel engraving REALLY oughtta be marked as such, alerting the user to be careful what he feeds it. "Tactical" type rifles are used in the field, in the mud, rain, snow and dust...not exactly a place where you want "benchrest" type cartridge fitment in the chamber. It needs to be able to tolerate adverse conditions.

3. If the chamber's body dimensions are so tight factory ammo won't fit, what sizing die is ever going to REsize cases to fit? Usually, a virgin case is as small as it's ever going to be, and no off-the-shelf sizing die is going to get it smaller than it was to begin with. So what kind of ammo was this chamber ACTUALLY intended for? Again, reference the above point concerning the conditions a field tactical rifle is subjected to.

4. Tactical type rifles use the heavier, longer, higher BC bullets available for the given bullet diameter. That usually means a longer throat. Usually, factory ammo is loaded with bullets more oriented towards sporting/hunting purposes, which are shorter and don't require as much throat. Also, factory ammo meets SAAMI specs, and SAAMI usually specifies a rather short COAL. For example, 2.800" for a short action cartridge. So short, light, low BC bullets loaded to a short SAAMI COAL won't fit in this rifles chamber??

Something is rotten in Denmark.

 

[Hoosier]

The gunsmith used a "tactical" chamber reamer. His words not mine. The rifle will chamber factory cartridges. It was my mistake because when the bolt seemed tight on closing I stopped. After talking to the gunsmith, he said the throat was intentionally chambered short, and when loading the rifle the bolt would be tight. I have plenty of room to adjust the seating depth of the projectiles.
Hoosier

 

[firearmdoc1]

I would pull apart a factory load and see if the case will chamber without resistance. If it doesn't than you certainly don't have a proper chamber. If it does chamber without resistance, you need to determine how deep your bullets need to be seated. DO NOT re-seat factory loaded ammo. Pull the bullets and work up your own loads.
If I were talking to a gunsmith who claimed to use a" tactical reamer", I would thank him for his time and find a new smith.

 

[Hoosier]

Rifle shoots great. It's consistent shooting under 1MOA at 100yds. I have one group under an inch at 200yds.
Hoosier

 

[gunsandgunsmithing]

Sounds to me that it's throated as to be able to reach the lands with ammo loaded to magazine length. I don't know what bullet the smith used as a baseline for this and the ideal amount of freebore to do so will be different with different bullets. Short actions won't allow "ideal" bullet seating, where the top of the boat tail is just above the neck/shoulder junction with a 7wsm with most of the high bc bullets due to mag length. So, to make the round fit the magazine we must seat the bullets deeper into the case. What your smith has done is a good thing IMO, assuming everything else is done correctly. He or another smith could always throat it longer with a throating reamer if you prefer. I'm doing the same thing for a .260 build I plan to shoot in the same kind of matches. I prefer to be able to reach the lands before running out of mag length. Just work your loads up carefully. You "may" run into pressure sooner in terms of powder charge, but velocities will probably be slightly higher with a given charge. Start low and work up, with a chronograph.