Accuracy issues - Page 2

Bart B. · November 24, 2019, 12:46 PM

I don't think muzzle velocity is the cause of this problem. As long as the barrel is reasonably clean.

A 100 fps change in a 308's muzzle velocity changes drop at 100 yards about 2/10ths inch.

Something about the rifle changed.

**Unclenick** · November 24, 2019, 11:48 PM

Ketch,

You can improvise the seating depth gauge. Search the forum for numerous methods of using cases for the job. Probably the most common is to sacrifice a case by splitting the neck from mouth to shoulder with a hacksaw, a Dremel cutoff wheel, or a slitting saw. Clean up the burrs. Press the slit part together enough to hang onto a bullet with a bit of friction. Seat a bullet of the type you are loading in just past the mouth. Push this into your chamber by hand until the case shoulder meets the chamber shoulder. This causes the throat of the chamber to seat the bullet. Use a cleaning rod coming in from the muzzle to push this dummy out without disturbing the bullet position in the case. Measure the COL and call it maximum for singly-loaded rounds in your chamber. As long as you load that length or shorter, cartridges will fit into the chamber.

Work up a load with the bullet out far like that, using charges ten percent smaller than the normal load range. That will compensate for the pressure increase caused by making throat contact. Once you establish a best load there, try seating the bullets to 0.02" shorter COL and then 0.04" shorter, and so on until you find the right seating depth for the smallest groups. Once you have that, you can return to adjusting the powder charge to shrink them further. Sometimes it turns out throat contact was best for your gun. Sometimes the best spot can turn out to be much further back; even an eighth of an inch or more. This depends mainly on the gun and cartridge and bullet combination. Choice of primer and powder affect it, too. Many find the best COL in that first step back, but it isn't always so. Many guns turn out to have two seating depth sweet spots: one long one for single-loading, and a shorter one suitable for magazine feed. You just have to try them and see.

GeauxTide · November 25, 2019, 11:01 AM

Could be the weather change. I use H4895 because it's the Extreme (temp insensitive). My load is 42gr under 165 Grand Slams and shoots 1/2". My old 788 barrel is rough, so I keep it clean, per Unclenik's comments. I had an old 700 in '06 that tightened up with a piece of credit card between the forend and barrel.

ammo.crafter · November 25, 2019, 11:28 AM

What is the length of your resized brass?
What is your COAL after loading?
Do your reloads enter the chamber easily or do you have to exert a bit of forward pressure to chamber?

Are you full sizing brass or neck sizing?
Do you square the case mouth before seating?
Do you champher the case mouth after cutting the case to specs?

Try firing at 100yds; 125yds; 150yds, etc and see where the change occurs.

Good luck.

Ketch · November 25, 2019, 02:25 PM

Quote:

Originally Posted by ammo.crafter

What is the length of your resized brass?
What is your COAL after loading?
Do your reloads enter the chamber easily or do you have to exert a bit of forward pressure to chamber?

Are you full sizing brass or neck sizing?
Do you square the case mouth before seating?
Do you champher the case mouth after cutting the case to specs?

Try firing at 100yds; 125yds; 150yds, etc and see where the change occurs.

Good luck.

I’d love to give you that information off hand but it’s in my reloading notebook that’s currently packed up. I’m in the process of building a house and am slowly packing things up and that was one of the first things in my shop to get packed up.

What I do have is:
Yes my reloads enter the chamber easily

I full size when I do a mass run and then I neck size until they start to stretch too much and become tight (usually 2-3 reloads)

I have an RCBS trimmer that squares them for me when I need to trim them down

Yes I champher the case mouth

The range I go to does not allow me to bring my own target stands I can shoot at 25-50-100-200-300 that’s it.

603Country · November 25, 2019, 05:45 PM

The OP sounds like a knowledgable reloader. I doubt it’s the reloads, unless he just has the wrong powder and bullet combo.

I’d swap out the scope. I’ve had two puzzling accuracy problems that turned out to be scope problems. Worse, the first time was with a new rifle and scope, and the scope was bad. I had no history of good loads with that rifle, so was starting from zero. I burned a lot of powder and wasted many bullets and just kept getting random groups. Somebody suggested another scope and that solved the problem eventually.

If good groups start to open up, it usually turns out to be a fouled bore. If cleaning the bore doesn’t fix the problem on a heretofore trusted accurate rifle, I start thinking it might be the scope or mounts

November 24, 2019, 11:48 PM	#27
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Ketch, You can improvise the seating depth gauge. Search the forum for numerous methods of using cases for the job. Probably the most common is to sacrifice a case by splitting the neck from mouth to shoulder with a hacksaw, a Dremel cutoff wheel, or a slitting saw. Clean up the burrs. Press the slit part together enough to hang onto a bullet with a bit of friction. Seat a bullet of the type you are loading in just past the mouth. Push this into your chamber by hand until the case shoulder meets the chamber shoulder. This causes the throat of the chamber to seat the bullet. Use a cleaning rod coming in from the muzzle to push this dummy out without disturbing the bullet position in the case. Measure the COL and call it maximum for singly-loaded rounds in your chamber. As long as you load that length or shorter, cartridges will fit into the chamber. Work up a load with the bullet out far like that, using charges ten percent smaller than the normal load range. That will compensate for the pressure increase caused by making throat contact. Once you establish a best load there, try seating the bullets to 0.02" shorter COL and then 0.04" shorter, and so on until you find the right seating depth for the smallest groups. Once you have that, you can return to adjusting the powder charge to shrink them further. Sometimes it turns out throat contact was best for your gun. Sometimes the best spot can turn out to be much further back; even an eighth of an inch or more. This depends mainly on the gun and cartridge and bullet combination. Choice of primer and powder affect it, too. Many find the best COL in that first step back, but it isn't always so. Many guns turn out to have two seating depth sweet spots: one long one for single-loading, and a shorter one suitable for magazine feed. You just have to try them and see. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

November 25, 2019, 11:28 AM	#29
ammo.crafter Senior Member Join Date: June 25, 2006 Location: The Keystone State Posts: 1,970	huh? What is the length of your resized brass? What is your COAL after loading? Do your reloads enter the chamber easily or do you have to exert a bit of forward pressure to chamber? Are you full sizing brass or neck sizing? Do you square the case mouth before seating? Do you champher the case mouth after cutting the case to specs? Try firing at 100yds; 125yds; 150yds, etc and see where the change occurs. Good luck. __________________ "Peace is that brief glorious moment in history when everybody stands around reloading". --Thomas Jefferson

November 24, 2019, 12:46 PM	#26
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	I don't think muzzle velocity is the cause of this problem. As long as the barrel is reasonably clean. A 100 fps change in a 308's muzzle velocity changes drop at 100 yards about 2/10ths inch. Something about the rifle changed.

November 25, 2019, 11:01 AM	#28
GeauxTide Senior Member Join Date: April 20, 2009 Location: Helena, AL Posts: 4,424	Could be the weather change. I use H4895 because it's the Extreme (temp insensitive). My load is 42gr under 165 Grand Slams and shoots 1/2". My old 788 barrel is rough, so I keep it clean, per Unclenik's comments. I had an old 700 in '06 that tightened up with a piece of credit card between the forend and barrel.

November 25, 2019, 05:45 PM	#31
603Country Senior Member Join Date: January 6, 2011 Location: Thornton, Texas Posts: 3,998	The OP sounds like a knowledgable reloader. I doubt it’s the reloads, unless he just has the wrong powder and bullet combo. I’d swap out the scope. I’ve had two puzzling accuracy problems that turned out to be scope problems. Worse, the first time was with a new rifle and scope, and the scope was bad. I had no history of good loads with that rifle, so was starting from zero. I burned a lot of powder and wasted many bullets and just kept getting random groups. Somebody suggested another scope and that solved the problem eventually. If good groups start to open up, it usually turns out to be a fouled bore. If cleaning the bore doesn’t fix the problem on a heretofore trusted accurate rifle, I start thinking it might be the scope or mounts