question on odd results

[imaguy3]

I haven't been reloading too long, but it's been my experience (and was taught to me), that looking for a velocity node is a good start to finding an accurate load. The process worked well on 2 bolt guns I've loaded for, found a node, had SD in the single digits, and was 1/2" moa without fuss.

Finally started doing load development on my Grendel. My guns shoots Factory loaded SST a little over MOA as of late. I established a baseline with factory ammo, 5 shot group, 2410 fps (sd13) and 1.2moa.

Using the same 123gr SST bullet, Fed. GMM ar primers, IMR 8208xbr powder, and all once fired brass I loaded up a bunch of rounds to find a velocity node, to the same base to ogive length measurement as factory ammo. I found a node at 28.2g (or so I thought).

Loaded up 10 of them today, went out and shot 2 5 shot groups with it. I produced a 10 shot combined velocity of 2447fps and SD of 6. I thought I was on the mark (low sd = small groups I thought) until I looked at the groups and saw one was 1.8 moa and the other was 2 moa.

Loaded up some American Gunner to check my gun wasn't messed up... those 5 shots came in at 2399fps, SD of 20, and a 1.1 moa group

Anyone experience good numbers but bad groups before... without it being caused by the gun (proofed by my factory ammo shooting normally)? Any advice?

[Popeye212]

It has been my experience that low SD doesn't always mean small groups. I have had double digit SD's with small groups. I have had VERY LOW Sd's with by my standards unacceptable groups. Trick is to find a load where they coincide.

[imaguy3]

It has been my experience that low SD doesn't always mean small groups. I have had double digit SD's with small groups. I have had VERY LOW Sd's with by my standards unacceptable groups. Trick is to find a load where they coincide.

yea... guess in my limited experience I've just noticed they coincided.. and SD on factory ammo always sucked... Guess I wasn't in the node I thought I was...

[Popeye212]

yea... guess in my limited experience I've just noticed they coincided.. and SD on factory ammo always sucked... Guess I wasn't in the node I thought I was...

I wish and hope that in the rest your experience they will all coincide... Course then it might get boring.

[grayfox]

I haven't been reloading too long, but it's been my experience (and was taught to me), that looking for a velocity node is a good start to finding an accurate load. The process worked well on 2 bolt guns I've loaded for, found a node, had SD in the single digits, and was 1/2" moa without fuss.

Finally started doing load development on my Grendel. My guns shoots Factory loaded SST a little over MOA as of late. I established a baseline with factory ammo, 5 shot group, 2410 fps (sd13) and 1.2moa.

Using the same 123gr SST bullet, Fed. GMM ar primers, IMR 8208xbr powder, and all once fired brass I loaded up a bunch of rounds to find a velocity node, to the same base to ogive length measurement as factory ammo. I found a node at 28.2g (or so I thought).

Loaded up 10 of them today, went out and shot 2 5 shot groups with it. I produced a 10 shot combined velocity of 2447fps and SD of 6. I thought I was on the mark (low sd = small groups I thought) until I looked at the groups and saw one was 1.8 moa and the other was 2 moa.

Loaded up some American Gunner to check my gun wasn't messed up... those 5 shots came in at 2399fps, SD of 20, and a 1.1 moa group

Anyone experience good numbers but bad groups before... without it being caused by the gun (proofed by my factory ammo shooting normally)? Any advice?

good consistent MV and low SD but bad groups usually means the timing of the bullet's exit is off. Try that load but varying OAL by 0.010 delta's... this will change the timing of bullet exit from the muzzle, and one of those OAL's will have a better group size than the others. Since there is a longitudinal pressure wave running down and back the barrel at 18,000 ft/sec, a difference of a few microseconds (the 0.010 seating shift) can have a big effect on your group size.
Of course... could be you were having a not-so-good cheek weld day, too...! We've all been there.

[Kswhitetails]

Another thing to remember, the AR isn't a bolt. There are a few more variables to consider when shooting one. The action, bolt face lockup, and chamber are all typically more "loosely" toleranced. The idea is ease of loading and extraction, therefore the tight chamber usually machined into 1/2 moa bolt guns cause feeding and extraction problems in a semi-auto. Magazines are less exact, and switching from one to another can actually cause a difference. Your low SDs and velocity look great. But, I don't know how much that means in an AR. The bolt gun has a captured gas vessel that remains static until your bullet exits, when the gasses can escape. The AR scavenges gas volume and pressure well before the bullet exits. I've had many of my best groups on my AR with an SD in the 30s... Bullet timing and harmonics are the real gremlins here, mainly because the other variables are so exaggerated and impossible to control. I've learned that I settle for 1-1.5 moa and call that good on my gas guns. If I want better, I go to my Impact 737.

GF has it ^^.

[imaguy3]

No reason to settle for 1moa in a gas gun... I dropped down to my lower velocity node, 2356fps with an sd of 9... 5 shot group at 90 yards... I'm thinking what I thought was a node at book max was just a fluke... Gonna play a touch with seating depth but this should do fine...

[A5BLASTER]

No reason to settle for 1moa in a gas gun... I dropped down to my lower velocity node, 2356fps with an sd of 9... 5 shot group at 90 yards... I'm thinking what I thought was a node at book max was just a fluke... Gonna play a touch with seating depth but this should do fine...

I couldn't live with that.

I would revisit the faster node and change the seating depth and shoot the new depths in separate groups of 5 rounds each .

Main reason why your load is diffrent then the factory load is your useing diffrent powder, primer and brass then the factory round does.

That are get rid of the 8208 and go with cfe223, leverevolution.

[imaguy3]

I couldn't live with that.

I would revisit the faster node and change the seating depth and shoot the new depths in separate groups of 5 rounds each .

Main reason why your load is diffrent then the factory load is your useing diffrent powder, primer and brass then the factory round does.

That are get rid of the 8208 and go with cfe223, leverevolution.

I'm using the same brass as the factory hornady SST, shooting is how I sourced it. Yes powder and primer are different.

How much can you really change seating depth? How much past the cannelure can you seat the SST? I can only seat further in as I'm at mag length, I would be nervous about seating too deep when I'm already at book max. I didn't see pressure signs but people warn about 8208 spiking?

When I was working up loads on bolts guns and messing with depth, I have never seen a group go from 2moa to 1/2 just from seating depth..

I specifically chose 8208 for temp stability, I don't believe either of those other powders are, correct?

I'm currently loading the ogive at .045" off the lands.

[A5BLASTER]

I'm using the same brass as the factory hornady SST, shooting is how I sourced it. Yes powder and primer are different.

How much can you really change seating depth? How much past the cannelure can you seat the SST? I can only seat further in as I'm at mag length, I would be nervous about seating too deep when I'm already at book max. I didn't see pressure signs but people warn about 8208 spiking?

When I was working up loads on bolts guns and messing with depth, I have never seen a group go from 2moa to 1/2 just from seating depth..

I specifically chose 8208 for temp stability, I don't believe either of those other powders are, correct?

I'm currently loading the ogive at .045" off the lands.

What's your coal length now?

Do 5 rounds at 5 thousands shorter and 5 rounds at 10 thousands shorter and 5 rounds at 15 thousands shorter.

I wouldn't worrie where the cannelure lands at. If you can't go longer then you have to go shorter in seating to get the bullet travel time in tune with the barrel whip.

Until you find that seating depth your faster node will show good sd and es and have bad groups like they do now.

I start all my loads at 10 thousands off the lands unless they contact the lands outside of what fits the mag.

I work up in 2 or 3 tenths till I find what's max for my rifle. Then I look at the lower nodes and fins the one with the tightest sd and es. Then I load at that powder charge but go 5 thousands shorter every 5 rounds till I'm 20 thousands shorter then I started.

Doing it like that has worked for me. It's the principals behind the barrel timing theory that Grayfox was talking about.

Works with all rifles.

Edit to add.

Cfe223 and leverevolution will have more speed then 8208. I live in Louisiana so temp stability isn't a worrie for me.

[imaguy3]

What's your coal length now?

Do 5 rounds at 5 thousands shorter and 5 rounds at 10 thousands shorter and 5 rounds at 15 thousands shorter.

I wouldn't worrie where the cannelure lands at. If you can't go longer then you have to go shorter in seating to get the bullet travel time in tune with the barrel whip.

Until you find that seating depth your faster node will show good sd and es and have bad groups like they do now.

I start all my loads at 10 thousands off the lands unless they contact the lands outside of what fits the mag.

I work up in 2 or 3 tenths till I find what's max for my rifle. Then I look at the lower nodes and fins the one with the tightest sd and es. Then I load at that powder charge but go 5 thousands shorter every 5 rounds till I'm 20 thousands shorter then I started.

Doing it like that has worked for me. It's the principals behind the barrel timing theory that Grayfox was talking about.

Works with all rifles.

Edit to add.

Cfe223 and leverevolution will have more speed then 8208. I live in Louisiana so temp stability isn't a worrie for me.

My OAL is 2.245.

I live in So. Az... right now it's 106*, in 2 mths when I'm deer hunting it will be 40*... I like temp stable haha

[Lemonaid]

Imaguy3, one option is to play with the barrel harmonics and see if your good SD loads will get the accuracy you want.
The most easy way is to buy a jam nut, scribe some lines on your muzzle devise (10 lines 1/10 rotation each) and vary how much it's threaded in or out.
Method two is to vary the amount of torque on the barrel nut.
Method three is a deresonater at different length amounts of the barrel.
Method four screw(s) through the hand guard that can put some upward tension on the barrel.

[grayfox]

If he likes the lower node good for him. There are however, several other variables at play here, but the one observation I'll make is that the sst, in my experience, is not real jump sensitive, liking typically to be around 2.245.

If your 2.245 is 0.045 off the lands then there's a good chance your chamber is a short one. Might be this is the best you can do with that limitation.

[imaguy3]

Well I just shot a couple groups at diff. depths. Using the 28.3 charge, setting the bullet back further... at 0.020" shorter than previously, my group shrank from 1.8-2 moa to a consistent 1.1-1.2 moa... I'm gonna load up some more a little deeper and see if I can get it any better... Currently it's 0.065 off the lands... I'm hoping that setting back helps it more, I had a 30-06 a few years ago that loved having Bergers set 0.08 off the lands... so maybe?

[rabiddawg]

I live in Louisiana so temp stability isn't a worrie for me.

That’s exactly the reason I use imr 8208. It’s 100 degrees out now. It is not unusual for it to be 25 during hunting season.