Range Report 175 FGMM .308 - unexpected results at 600 yards

[gannon145]

I was at my club yesterday getting certified to fire on our 600 yard range and was very puzzled with my results. I'm hoping to have some light shed on what I am missing.

Rifle: Rem 700 ADL 26 in barrel
Scope: Vortex 6-24 HS XL FFP
Ammo: FGMM 175 (2600 fps)

So the qualifying was in 2 stages, 200 yards to prove you have a 200 yard zero. Then back at 600 yards to show you know your come up and are technically capable.

At the 200. Put 5 a little low in the X ring and decided that was more than enough at that rage. My zero was done on a bench and this was from prone, so the fact that it was in the lower half of the X ring (1/2 MOA low maybe) was understandable.

At the 600. Here's where I get thrown for a loop. Running 2 different ballistics programs (shooter and ballistic ae) I end up with a come up of 13.5 MOA for 600 yards. So I dial it in, take my shot.... and wait what, almost 20 inches (3 MOA) low. Ok, I flinched or something. Spotter calls for another shot, exact same spot. So I make my 3 MOA adjustment up to 16.5 MOA and put one at 11 o'clock just outside the X ring.

Luckily they didn't hold it against me and I qualified, but I was very confused. I know factory loads aren't know for extreme consistency, but FGMM has a pretty good reputation. So I plugged my results into both of my ballistics programs and they output that my fps is actually 2377/2410 depending on which program I looked at. So basically 200 fps lower than the advertised 2600 fps. Now remember I'm shooting a 26 in barrel, so no loss there...

So what the heck is going on? Are my calculations messed up? Should I check the gun? Is it normal?

Any insight will be greatly appreciated.

 

[sinister]

Factory Remington barrel, probably with the standard ungodly-long throat giving you gas blow-by and dropping your velocity. Probably not helping your standard deviation, either.

 

[EXTREMEPREJUDICE]

Well, using Ballistic AE I have a come up of 14.8 MOA and if you were .5 MOA low at sight in that amounts for a difference combined of almost 2 MOA. Add in environmental factors DA, wind, etc. that could easily adjust for another 1 MOA and also your sight height, base, etc.. Finally, you can never use published ammo FPS as gospel because it can vary quite a bit in your rifle. Of course, we are addressing variances between ballistic calculators and results, not considering shooter error.

 

[Gray]

finally, you can never use published ammo fps as gospel because it can vary quite a bit in your rifle. Of course, we are addressing variances between ballistic calculators and results, not considering shooter error.

^^^ this!!

 

[Timo Turl]

At the 200. Put 5 a little low in the X ring and decided that was more than enough at that rage. My zero was done on a bench and this was from prone, so the fact that it was in the lower half of the X ring (1/2 MOA low maybe) was understandable.d.

This is something to consider. 5 a little low off a bench and then you find yourself low at 600....i agree factory ammo isn't perfect but your approach is off too. Get 5 perfect from prone at 200 and then try it again.

 

[gannon145]

Factory Remington barrel, probably with the standard ungodly-long throat giving you gas blow-by and dropping your velocity. Probably not helping your standard deviation, either.

Ok thanks, I'm just really surprised by that much of a difference. I guess if the consistency isn't too awful I'll still just burn out this barrel before switching to 260.

Well, using Ballistic AE I have a come up of 14.8 MOA and if you were .5 MOA low at sight in that amounts for a difference combined of almost 2 MOA. Add in environmental factors DA, wind, etc. that could easily adjust for another 1 MOA and also your sight height, base, etc.. Finally, you can never use published ammo FPS as gospel because it can vary quite a bit in your rifle. Of course, we are addressing variances between ballistic calculators and results, not considering shooter error.

All environmentals were factored in as well as gun setup.

This is something to consider. 5 a little low off a bench and then you find yourself low at 600....i agree factory ammo isn't perfect but your approach is off too. Get 5 perfect from prone at 200 and then try it again.

I hear what you're saying but I only had access to a bench for zero'ing. Had to go through this qualification before I was allowed to shoot prone on the 600 yard range. Bench zero and prone zero tend to be different, I was just pointing that out. I will make the correction if it continues to manifest in prone. Thanks for the input though.

 

[40xs]

For what it's worth 16 moa is fairly standard from a 100yd. zero for 600yd. X using factory equipment and bullets. And for future reference about 37 moa is good for 1000yd using the same equipment and the 175gr.

 

[gannon145]

For what it's worth 16 moa is fairly standard from a 100yd. zero for 600yd. X using factory equipment and bullets. And for future reference about 37 moa is good for 1000yd using the same equipment and the 175gr.

Zero was 200. Confirmed 15 min before shooting at 600 yards. I would have thought the same thing if I didn't shoot at 200 just before going to 600.

I have some 168s and A-Max 155s that I'm going to try out and see what results I get.

Factory Remington barrel, probably with the standard ungodly-long throat giving you gas blow-by and dropping your velocity. Probably not helping your standard deviation, either.

Is this a common problem with stock 700s?

 

[40xs]

Well, Gannon, When you think about it, zero from 100yd. to 200 yd is only 1.5 min. So we'er still in the range of 16 moa at 600. 1/2 moa at 600 is only only 3 inches and still in the X ring or well within the 10 ring.

 

[gstaylorg]

I've been playing around with some FGMM 175s the last couple weeks in a GAP rifle I just got back from being re-barreled. Out of the 30" 11-twist barrel, the FGMM 175s are pushing an avg. MV of 2754 fps, measured with a MagnetoSpeed chronograph. With the correct atmospheric inputs, JBM gave me a predicted drop for that MV of 13.8 MOA at 600 yd. My actual drop was very close to dead on at 13.875 MOA; obviously I couldn't go any finer with 0.125 MOA turrets. The JBM predicted drop at 1000 yd for that MV was 34.1 MOA, at a 1000 yd match this past weekend, the actual drop ranged from 33.875 to 34.375 MOA, depending on wind/temp conditions for that specific string. In my hands, JBM predicted drops have been extremely close to actual drops as long as I input the correct atmospheric data. Although I can't speak about the ballistic prediction algorithms you used, my overall take is that they are generally much closer than the 3.0 MOA error you described, as long as you correctly input the rifle-specific, MV, and atmospheric data.

Based on this, my best guess is that you have one of two things going on. First (and most likely), your MV is not 2600 fps. Second, your turret adjustments are not what you think they are. The first you can determine by actually measuring the MV with a chronograph. The second you can determine by doing a box test to make sure your turrets adjustments move your POI as they should.

 

[gannon145]

Based on this, my best guess is that you have one of two things going on. First (and most likely), your MV is not 2600 fps. Second, your turret adjustments are not what you think they are. The first you can determine by actually measuring the MV with a chronograph. The second you can determine by doing a box test to make sure your turrets adjustments move your POI as they should.

Yea that is what I'm worried about. I don't have a chronograph to check against unfortunately. I did a box test with the scope when I first got it and it tracked ok. I haven't dropped it or anything since so I wouldn't think there would be an issue. I'll try and do another one next time I'm at the range just to rule it out though.

I've shot this rifle at 600 before with FGMM 168s. I went back and checked my data book and was making hits with 13.5 Up. What would cause FPS loss with 175s and not with 168s? Is the OAL different between the 2 rounds and would that matter?

Could I have a bad batch of 175s? I've had some other ammo show up since this issue popped up. Unfortunately no other 175s but I guess I'll just go out and try the other brands and see what happens.

 

[40xs]

Remember, 4" more of barrel and 150fps higher vel. will make up the difference in moa. 34 moa sounds right for high end of 2700 and 175 gr. I've got a 29" and am at 29 moa with a 185 Berger jug. at 1000. the bullet, the barrel. the load, ambient temp. and the elevation above sea level all play a part on your zero. I've seen over a moa difference from morning to afternoon. that's why we keep notes on all the above.