Long OAL .308

[thepatchcable]

I measured my OAL with a 155g bullet which comes out to 2.88. This is a gas gun semi-auto.

Can I use a COAL of 2.85 with a the minimum charge weight listed by the MFC and be OK? 2.8 seems extremely short if I follow the standards.

Or will this increase pressure with more volume in the case (but no extra powder)?

 

[nn8734]

Use whatever COAL that will fit and feed reliably from the mag then start at a low charge weight and work up. Stop when you see pressure signs…mess around with seating depth until it groups to your liking…that’s it.

What 155g bullet are you using?

 

[thepatchcable]

Use whatever COAL that will fit and feed reliably from the mag then start at a low charge weight and work up. Stop when you see pressure signs…mess around with seating depth until it groups to your liking…that’s it.

What 155g bullet are you using?

Hornady 155 HPBT

 

[camocorvette]

Where did you get your OAL of 2.88? Is this a load from a bolt gun? A load you just threw together?
Like stated. Load to mag length that will feed reliably. Gas guns will exhibit pressure sooner then a bolt gun.

 

[thepatchcable]

Where did you get your OAL of 2.88? Is this a load from a bolt gun? A load you just threw together?
Like stated. Load to mag length that will feed reliably. Gas guns will exhibit pressure sooner then a bolt gun.

An OAL gauge with a fire formed factory cartridge. Semi-auto gas.

 

[Doom]

I'm sorry but something doesn't sound right. From original post. First question are you measuring from the base of the case to the tip of the bullet? Or are you measuring from the base of the case to the shoulder on the case? Verify this is a 308? Post #5 what OAL gauge are you using? Did you zero your caliper with the case gauge attached? How are you measuring OAL on a fired cartridge?

Is the OAL of 2.880 the measurement you get seating the bullet to the lands?

 

[thepatchcable]

I'm sorry but something doesn't sound right. From original post. First question are you measuring from the base of the case to the tip of the bullet? Or are you measuring from the base of the case to the shoulder on the case? Verify this is a 308? Post #5 what OAL gauge are you using? Did you zero your caliper with the case gauge attached? How are you measuring OAL on a fired cartridge?

Is the OAL of 2.880 the measurement you get seating the bullet to the lands?

I'm measuring the COAL (base to bullet tip). I know this isn't as accurate but waiting on a comparator to arrive so I can measure CBTO/BTO. I'm using Hornady's Overall Length gauge. So my COAL is 2.88 to the lands (with a bullet seated) but I'm setting COAL for 2.85. So I'm about .020 off the lands.

 

[Doom]

OK, so that clarifies thinks quite a bit, at least for me. Going longer than 2.800" or 2.810" COAL (cartridge overall length) sometimes allows more powder before you get pressure signs but it doesn't really affect the load data. That 155 bullet probably will shoot very well at those lengths. Trying to put it near the lands in a semi auto might be a problem. As noted above if you intend to feed from a magazine it may not fit and even if it does you may have feed issues since the feed ramp will engage the bullet earlier in the feed cycle. You may have failure to feed or bullet setback.

 

[camocorvette]

Yeah was just gonna say depending on the mags you use, you won't get that to load from a mag.

 

[thepatchcable]

Yeah was just gonna say depending on the mags you use, you won't get that to load from a mag.

My rifle has large mags around 2.9 I think. I know they can hold 2.85 reliably.

 

[thepatchcable]

OK, so that clarifies thinks quite a bit, at least for me. Going longer than 2.800" or 2.810" COAL (cartridge overall length) sometimes allows more powder before you get pressure signs but it doesn't really affect the load data. That 155 bullet probably will shoot very well at those lengths. Trying to put it near the lands in a semi auto might be a problem. As noted above if you intend to feed from a magazine it may not fit and even if it does you may have feed issues since the feed ramp will engage the bullet earlier in the feed cycle. You may have failure to feed or bullet setback.

Thanks! Yeah, I know my mags can feed reliably @ 2.85. Now I can work up my load and can then adjust seating depth.

 

[camocorvette]

Okay. I think KAC and ACS are the best for long oal from what I've read.
And to your original question.
If you develop a load in a case that's OAL of 2.85 and then use the same load and shorten length to 2.80 it will increase pressure. How much? Don't know. I would drop down some though.

 

[918v]

I measured my OAL with a 155g bullet which comes out to 2.88. This is a gas gun semi-auto.

Can I use a COAL of 2.85 with a the minimum charge weight listed by the MFC and be OK? 2.8 seems extremely short if I follow the standards.

Or will this increase pressure with more volume in the case (but no extra powder)?

Load data is based on a 2.8” coal.

If you increase the coal the pressure will decrease. More volume in the case with the same amount of powder means less pressure. So if you use a longer coal with the minimum load listed in the manual it may not cycle.

Another consideration is case weight. A heavier case than the one used in the manual will increase pressure (due to the reduced volume) so that in itself will make up for the pressure reduction due to the longer coal.

 

[OkieMike]

Some bullets are picky about how far they jump. Others are very forgiving. I don't have any experience firing Hornady HPBT bullets yet... More on that in just a second... but Sierra MatchKings have been very jump tolerant for me.

Coincidentally, I recently loaded some of the Hornady 155 HPBT with Varget in Peterson brass... Planning to shoot them tomorrow. Mainly a pressure test but I'm curious to see if they show any promise.

Mike