Hornady 178s causing pressure signs

[MK20]

Hornady 178 BTHP are causing pressure signs in my 308 AT. They are being loaded in LC LR brass with 41.7 grains of 4064 and a S&B primer. They come out at 2550 fps. I am getting stiff bolt lift and mild ejector swipe.

FGMM 175 SMK shoots in the same gun same day at 2725 with 43.3 grains of powder of some type with absolutely no pressure signs.

I pulled and swapped bullets between the FGMM and my reloads. The problem traveled with the Hornady bullet. Anyone know why this bullet would be causing pressure signs?

It seems very weird to me.

 

[KZP]

Are you loading 178 and 175 to the same OAL? Measure the 178 bullet and the 175 length, could be you are losing case capacity if the 178 is longer and loaded to same OAL as 175.

 

[MK20]

Yeah. I am loading them both as long as I can for mag length in other rifles. It shouldn't be that much difference. The FGMM is coming out at 2725 after all with NO pressure signs at all.

 

[MK20]

I also messed around with seating depth with the 178 and it didn't change much. I ran it in another 200 thou and no change, lol so it can't be seating depth.

 

[DIBBS]

Possibly a difference in bearing surface, maybe slight difference in bullet diameter, jacket material etc.

It's always best to rework loads when changing any component or a new lot of bullets. JMHO

Drop back half a grain or a grain and work back up and see if it alleviates the problem.

 

[Rob01]

How far off the lands are you now?

 

[Mike Casselton]

I can swap the 168 Sierra and the 168 Nosler CC without issue. If I substitute the Hornady, the pressure skyrockets. It takes a 2 grain drop in powder charge to get me back to the same velocity.

Rework your load.

 

[MK20]

Interesting. Thanks for that info.

 

[Baddog 0302]

I'm going to make a SWAG and say it might be your weapon. I say that after doing dome research on the 178 ELD-M.
Hornady 's # 11 manual** lumps their 178's & 180's together and max's them out at 2500 fps with 41.7 4064, as well as 2520,TAC & 748.
** I think it's a general condescension that most ^ manuals are on the "lite" side. The exceptions are the Hodgdon online site and the Lyman Precision Rifle manual.

 

[Baddog 0302]

43.3 Gn. of a powder? what does it look like ? Do you have a Manufacturing date on your FGGM ammo ? Seams I read somewhere that ATK who produces Fed. ammo, also produces LCLR ammo, and also owns Alliance {the powder Co} and while they use their own blend of powder in the GMM ammo. they were using RL-15 in the LCLR ammo and for a while it was causing the M-14 sniper rifles a lot of grief in 115* weather.

 

[MK20]

It looks like RL 15 but is probably their proprietary blend.

 

[MK20]

It is 2016 headstamp

 

[MK20]

But 43.3 is right at what M118 LR is loaded with for RL 15.

 

[Rob01]

How far off the lands are you now?

?

 

[MK20]

I don't have the equipment to accurately check right now but I have played with the seating depth quite a bit and it didn't change the pressure signs.

 

[308pirate]

I don't have the equipment to accurately check right now but I have played with the seating depth quite a bit and it didn't change the pressure signs.

You need to figure out how much of each of those two very different bullet designs are intruding into the case volume. I will not be surprised in the least to find out that the Hornadys are eating up more case volume than the Sierras that come with FGMM and that will absolutely change the pressure dynamics.

Since you're loading to mag length I seriously doubt the bullets are anywhere near the lands.

 

[straightshooter1]

I don't have the equipment to accurately check right now but I have played with the seating depth quite a bit and it didn't change the pressure signs.

What's the COAL you're loading to to get to your mag length?

It was asked before, but you must of missed that question? We're all flying blind without the detailed measurements of your cartridge. But . . .

The 175 SMK is not near as long as the 178 Hornady BTHP. This is the most significant factor for and increase in pressure. The 178 is heavier, which also adds to pressure when keeping the same powder charge. These two things in addition to the cases being somewhat near maximum pressure with the SMK's leaves very little room before getting to the high pressure state. LC brass has substantially less volume than Federal brass, which will also contribute to the high pressure issue.

Bottom line is, when going from 175 SMK to 178 Hornady BTHP, there's a .085" difference in seating depth when both a loaded to the same COAL. Being .085" deeper in the case means one needs to lower the powder charge just on this point alone (not considering the additional weight of the bullet, which should also mean lowering the powder charge some to keep pressure down).

You mentioned 2550fps with the high pressure, which simply doesn't make any since. The only conclusion from that is that probably having to do with some misreading from your Chrono. It happens.

 

[MK20]

2550 is a 5 shot average with a magnetospeed. I then shot a 5 shot average with FGMM and got 2725. I doubt my chrono is wrong.

COAL is 2.880 or whatever is standard mag length. Going off of memory right now as I don't have my book in front of me.

 

[918v]

2550 is a 5 shot average with a magnetospeed. I then shot a 5 shot average with FGMM and got 2725. I doubt my chrono is wrong.

COAL is 2.880 or whatever is standard mag length. Going off of memory right now as I don't have my book in front of me.

When you varied coal, how short did you go?

 

[918v]

I'm going to make a SWAG and say it might be your weapon. I say that after doing dome research on the 178 ELD-M.
Hornady 's # 11 manual** lumps their 178's & 180's together and max's them out at 2500 fps with 41.7 4064, as well as 2520,TAC & 748.
** I think it's a general condescension that most ^ manuals are on the "lite" side. The exceptions are the Hodgdon online site and the Lyman Precision Rifle manual.

Most manuals are not on the light side. They spell out what their particular set of components did in their test gun. Second, Hornady list data to be used in their brass which is generally more spacious than LC.

 

[straightshooter1]

2550 is a 5 shot average with a magnetospeed. I then shot a 5 shot average with FGMM and got 2725. I doubt my chrono is wrong.

COAL is 2.880 or whatever is standard mag length. Going off of memory right now as I don't have my book in front of me.

I also use a MagnetoSpeed and I know they're very reliable . . . as long as they're mounted properly and the battery isn't too weak. With the numbers you've given and the physics of the internal ballistics, it just doesn't make sense. Something's just not adding up.

That COAL sounds about right and close to what I've used in the past. I'm convinced that the difference in seating depth of .085 and weight with the 178's is simply the cause of you're pressure signs.

 

[Baddog 0302]

Do you have any other powders suitable for loading the 308 with your 178's? The reason I ask is , I live on the water, with it being 100+ * in the sun, plus the threat of rain, I pretty much have the water free of boats and can load some of my 178 BTHP and se if I get any pressure signs from a 700 V with a 1-12 T barrel and a Tikka TAC W/ a 1-11 T. I'll try your 41.7 4064 plus anything else I have that you have. Won't be any speeds. just pressure signs on LR LR w/ 9 1/2's loaded to my P mag length. Could go longer for the Tikka , but that's not the length you have to deal with.

 

[Rob01]

2550 is a 5 shot average with a magnetospeed. I then shot a 5 shot average with FGMM and got 2725. I doubt my chrono is wrong.

COAL is 2.880 or whatever is standard mag length. Going off of memory right now as I don't have my book in front of me.

If you are loading them to 2.880" I bet you are jamming them into the lands. I just went and looked at my book and with the 178 BTHP I am in the lands at 2.163" from base to ogive. Factory loaded at 2.800" OAL is 2.097 base to ogive so at .066" to that 2.800" and you are at 2.866" so you might be jammed a good ways. I would seat those to about 2.820" OAL or about 2.117" base to ogive and try it again.

 

[supercorndogs]

My 178 a max load is 43.2g of RL15. I get ejector marks if go up to 43g of target with a 178 a max or 175 SMK. RL15 load is 2730, Varget load is 42.4 at 2620.

There are about a million different 308 chambers out there. My factory Remington barrel couldn't touch the lands with a 178 and keep the bullet in the case. My rifle from LRI, i can't remember which chamber, jams a 175 SMK at about 2.82.

 

[Baddog 0302]

How hard are your 178's to seat in your lc lr brass ? I started to load some 178's , both bthp & eld-m's in some lc lr cases and WTF ? COULDN'T seat them without a lot of force. YES, I had chamfered the inside of the necks.
Had some FGMM & Hornady Match brass handy so I tried them with the H 178 bthp. Easy to start and normal seating resistance.
Don't put a lot of stock on the Hornady OAL bullet tool, BUT here is what I found for OAL;
Tikka
178 HP, 2.9335
178 ELD M 2.8305
Rem 700 heavy barrel w/ 1-12T
178 HP , 3.0175
178 ELD M 2.9876

 

[Rob01]

Yup there are a lot of .308 chambers with differing freebore and why best to go shorter even down to factory 2.800" and try it so you know you are not jamming unless there is a chamber issue. The 178 BTHP does not mind a jump so load to factory OAL and check again for pressure.

And that seating difficulty is probably due to the die used and how much neck tension it gives. With the thicker necked LC brass it was probably giving a lot more neck tension than factory brass which it was set up for. That can be changed with a bushing die and being able to use a different bushing with different brass. I have mine set up like that and different bushings so I get .002" of neck tension with different brass.

 

[Doom]

The 178 length is 1.345” while the 175 is 1.240”. You say you are getting 2725 fps from FGMM. What barrel length?

 

[MNBob]

I have noticed that a dull neck chamfering tool creates a burr inside the neck. If you want consistent seating pressure you need to be sure your tools are cutting cleanly.