Is indexing a proven accuracy improver?

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  • Last Post 29 January 2017
John Alexander posted this 28 January 2017

When I started shooting CBs the conventional wisdom was that you should index both case and bullet for best accuracy.  So I started out doing it but it seemed unlikely that it worked and it was a PITÅ.  So I shot strings of groups alternating between groups with indexed and not indexed.  I couldn't see a difference in accuracy. So I stopped doing it and haven't indexed since.  However, I was shooting a factory rifle that would average about 1moa for 5 shot groups not a full bore custom benchrest rifle that would average near .5MOA. My experiments were also limited to 22 caliber bullets.

It has been a long time since I ran that experiment and discredited indexing for my own reloading.  But I still see indexing recommended in some writings about CB shooting.  Maybe it really does help in the rarefied zone of .5 moa or maybe my old experiment didn't involve enough groups and was misleading.

Has anybody shot comparison strings of index vs. non indexed rounds that indicated that indexing improved accuracy -- even a little?

John

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45 2.1 posted this 28 January 2017

I did this about in the early 90's. I was testing reloading methods in about 8 different 45-70 single shot rifles. Two of those rifles were worthy to shoot at very long range. The most accurate was a Navy Arms rolling block with a heavy octagon barrel. It liked the Saeco 1881 500 gr. RN. That rifle noticed no difference on how it was loaded and shot very well non indexed. It's contemporary was a Browning 1885 BPCR. That rifle liked a Hoch custom PB flat nose base pour bullet. That rifle gave 1 MOA non indexed and 1/2 MOA indexed, both case and bullet. These trials lasted about 18 to 20 months under all weather conditions. I found indexing works with some bullets in some rifles, but is not a guarantee of making something shoot better.

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JeffinNZ posted this 28 January 2017

I can see how indexing using a single shot rifle would be easy enough but how do you accomplish with a bolt gun?

Cheers from New Zealand

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RicinYakima posted this 28 January 2017

Other than one Trapdoor, all of my benchrest match shooting has been with Model 1903 Springfields. Using a fully expanded fired case I measure run out from just in front of the extractor cut to the mid-line of the neck. It varies from .003” to .010” between barrels / bolt combinations. My experience is that the less the run out, the less difference indexing makes. The more the run out, the greater the difference. Yes, I still orient bullet, case and chamber. No, I don't find it a PITA, as it only adds maybe 4 seconds per round to may normal reloading rate for match ammo.

Summer of 2004, IIRC, I loaded 940 rounds looking for the best dies and tools for reloading 30/06. Since I was doing this for myself, I only kept records in my field books, measuring with calipers from the target board. My estimate is that in all those 10 shot 100 yard groups, indexed gave about 1/10” better groups, with good dies. All cartridges were indexed.  Ammo with run out greater than chamber run out never shot well, i.e. 50% or larger than less run out groups.

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OU812 posted this 28 January 2017

Davis Tubb would index his cases. Marking the thin side of full length resized cases. He says thin side of case would stretch like a curved banana when fired, causing bullet to tip before entering rifling.

Turning necks and neck sizing only could prevent this curving of cases in a bolt action rifle.

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bucksnort925 posted this 28 January 2017

I shoot a Browning 1885 BPCR 40-65. Brass has no run out so I only have to index the bullet. Bullets have small dimple near tip. It does make a difference in accuracy, more notably for longer ranges.Does add more time in loading process but it is worth it.

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John Alexander posted this 29 January 2017

Ric,

I am confused.  Your first paragraph is about measuring runout of the rifles chamber -- right?

If you measure run out from one end to the other what is the case rotating on?  Maybe the two end points mentioned?

In your third from last sentence you say indexing was worth ten percent but in the second from last you say all cases were indexed.

Help please.

John

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RicinYakima posted this 29 January 2017

Sorry John, my writing is not as reveling as I thought. I used a case concentricity device made by Sinclair in about 2000, It has adjustable ball bearing “V” rests for the case. One end is set for the case just above the extractor groove, the second just about behind the should on the full diameter of the case. The dial indicator then reads off of the neck from center line of those points.

A really good Springfield '03 will average about 1 3/8” to 1 1/2” groups for ten shots at 100 yards. A good barrel will have fired cases that are within .003” run out and poor ones .010” run out. If you can make ammo straighter than the chamber, indexing doesn't matter. If your ammo is more crooked than the chamber, indexing helps some. My estimate is one ten of an inch (.10") on average of ten shot groups. Yes, I index bullet and cases and chambers all the time. Even if it doesn't really matter, if makes me feel confident.

I was testing reloading dies, and wrote the article published in The Fouling Shot ten years ago or so. No one questioned that indexing wasn't good in those days, so I never keep accurate group records, just field notes.

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John Alexander posted this 29 January 2017

Thanks for the explanation Ric.

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RicinYakima posted this 29 January 2017

Good commercial barrels and almost all custom barrels are better than any “Star Gauged” Springfield Armory barrel ever made. The skill of the workman who chambers the barrel is still the key, IMHO. Ric

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