OAL - Does this seem right?

[ekimerpud]

I am fairly new to hand loading. I've reloaded tons of handgun and shotgun rounds, but lately it's time to feed the bolt gun. I've gone as far as replicating Federal Gold Metal match and I am progressing to more advanced processes such as seating projectiles depth in relationship to the chamber. I have a .308 bolt gun from a very reputable company and it shoots 1/4 to 3/8 MOA with 168gr FGMM. I just recently bought a Hornady bullet comparator to measure bullet depth from ogive to back of the case and a Hornady OAL gauge to measure the bullet seating depth that just barely touches the lands in barrel. When I take the measurement from this rifle I get a measurement of 3.165" from back of case to ogive. When I measure factory FGMM, I get a measurement of 3.237. I'm no mathematician, but I'm pretty sure that means factory FGMM is seated .072" 'in the lands'!!!!! I measured both 10x and I'm pretty sure I'm measuring right (ex-machinist).

I have a couple questions:
1.) How concerned should I be with this?
2.) Do I run the risk of over pressure with FGMM?
3.) Should I send the rifle to the manufacturer for re-chambering?

Any advice or comments will be appreciated.

A Note: During a rifle class, a cease fire was called and I had issues (once) with unchambering a round. I had to slam the bolt up and back which resulted in the bullet staying lodged in the lands and powder spilling out everywhere. I punched the bullet out from the barrel with a cleaning rifle and it ran fine after. I assume this is from the bullet being seated in the lands and not behind.

Thanks,
Mike

 

[LawnMM]

did you zero the caliper after adding the gauge?

 

[muzzlebreaker]

When you measure with the OAL gauge, there is no way a .308 should be 3" long much less more.....the reason your bullet stuck when you unchamberd the round is a sure sign it is way too long and the bullet was barely seated into the case. Plus installing the comparator onto your calipers, closing the calipers and zeroing it out is how you measure your ogive and match it to the avg measurements given by the OAL gauge. My .308s seem to shoot best at an OAL of 2.799, measuring to the ogive is actually 2.14 if remember correctly, I dont have my data right in front of me, might be 2.17....any way your bullets sound way to long for .308. I have measured lots of factory ammo and of the top of my head Nosler Comp target .308 168gn were only 2.69" OAL. I'm surprised those even fit in the magazine much less let you close the bolt....NOT TRYING TO BE A JERK AT ALL AN NOT A 100% EXPERT.....but something just doesn't sound right

 

[ekimerpud]

I'm probably mis-using terminology (OAL is misused) or not articulating how I am determining the measurement. I didn't remove the length of the comparator or zero my calipers (I'm using dial calipers, not digital). The comparator is exactly 1.005. So...with that removed from my measurements above...all measurements from back of the case to ogive..

Factory FGMM = 2.232 ogive to back of case.

My Chamber = 2.160 ogive to back of case

which still means FGMM is seated .072 into the lands.

Hope that clears it up.. Any insight?

Thanks,
Mike

 

[GIXXER2000]

The only rifle I have seen have issues with un-chambering a round and having the bullets stick was a Savage. On 175 SMK factory FGMM I get an ogive of 3.215 and when I hand load 175 SMK with federal brass I set it at 3.270 so there is a significant difference in seating depth from factory to hand load. The COAL factory is 2.800 and my hand loads are 2.870.

 

[Twoboxer]

I'm probably mis-using terminology (OAL is misused) or not articulating how I am determining the measurement. I didn't remove the length of the comparator or zero my calipers (I'm using dial calipers, not digital). The comparator is exactly 1.005. So...with that removed from my measurements above...all measurements from back of the case to ogive..

Factory FGMM = 2.232 ogive to back of case.

My Chamber = 2.160 ogive to back of case

which still means FGMM is seated .072 into the lands.

Hope that clears it up.. Any insight?

Thanks,
Mike

LOL - doesn't change the issue you raised, which is the difference and its direction - but it did allow me to compare your measurements to my own 308.

I measured my "168gr FGMM" (Sierra 168 in a Lapua case) at 2.800 COL, 2.226 to the ogive. Given our tools and normal variation, that's certainly close enough to your 2.232 to say you measured that correctly.

AFAIK, that length should not put it into the the lands in a factory rifle.

That leaves us with : (a) you measured your chamber incorrectly (which I doubt in your case), (b) the chamber is very tight, perhaps purpose built for a smaller bullet or just wrong, or (c) if the round that got stuck was a reload (not an FGMM) it could be you made a bad one or few.

In any case, I'd paint (Sharpie) the tip of a reload with a base-to-ogive length of ~2.232, measure the OAL to the tip for reference, and chamber it. Look for scratches in the paint from the lands. If you see them, consider talking to the rifle maker with your hard evidence in hand. If it doesn't jam, I'd make some up that are longer (until I got the marks on the bullet) and figure out how I measured the chamber incorrectly.

 

[noylj]

COL: Cartridge Overall Length
Have you compared the factory bullet to the purchased bullet? Do you KNOW that your reloading bullets are the SAME as the factory bullets? Bullets of the same make/type/PN are made in different swage dies and can vary. Manufacturers change bullet designs without notification.
Pull some factory bullets and reload them. Determine max COL for the factory bullets (from the sounds of things you have already done this, but you have exceeded the max) and see if that is the same as the bullets you are reloading (take both bullets and re-do so you do the test at the same time).
As above, there is no question that a bullet stuck in the lede/leade/rifling means the COL was TOO long. This has been a well documented problem for about 100 years.
Duplicating factory ammo is almost a waste of time. If the factory ammo is accurate in your gun, and you have the exact same bullets as the factory uses, you still don't have the same powder, so you can't duplicate it.
All you can do is find the COL that works best with your component bullets and the powder(s) you have.

 

[LawnMM]

You can still zero a non digital caliper. If you mismeasured the OAL what's the chances you mismeasured the chamber length.

 

[KYpatriot]

Whoa guys...this isn't just a measuring problem. He had a round stick a bullet in the lands so hard it kept it when he unchambered...no question about it, your chamber is too short. OP, take it to a gunsmith and have it fixed. You don't even need to be anywhere near the lands with smks anyway, they will shoot great jumping a long way, and so will hybrids.

Load up a few DUMMY rounds such that it will comfortably fit in the magazine, call it .100 or so under mag length. This will get the bullet out of the case as far as possible yet still feed correctly. Load up 2or 3 of these, with the same case to ogive measurement, and take them to your smith, and tell them to chamber the rifle such that those rounds end up being ten thousandths or so off the lands. You never need to jam a tangent ogive bullet, and in my opinion with a tactical rifle you shouldn't jam any bullet just because of the potential of having the problem you had.

 

[ekimerpud]

Thanks for all the quick responses. I've contacted the smith and will be sending the rifle to them for inspection.

 

[Twoboxer]

Thanks for all the quick responses. I've contacted the smith and will be sending the rifle to them for inspection.

Please let us know what the outcome is

 

[Seandradamus]

Color the tip of a factory FGMM round with a sharpie then carefully chamber and extract if it is indeed jamming that muchyou should clearly be able to see the marks from the landS

 

[ekimerpud]

For those that were following. Smith confirmed the chamber was cut too short. Quick Turn around and all fixed. Thanks for the input.