B2 Chrome barrel accuracy

[Peter Laidler]

We had this 'chrome is best' palava with the 3 variants of 7.62mm Bren barrel and the papers relating to the trials were must reading on the relevant courses at Shrivenham. It was established beyond any doubt that chrome barrels are really for longevity. And that's the reason why the single barrel A4 version has just one barrel. The heat sink value and accuracy remained the same as the previous barrels (it didn't quite, depending on how the mixed results were interpreted, but it was minor blip.....) but the single chrome lined barrel - PROVIDED IT WAS CORRECTLY CHROMED to the Delloro spec - lasted as long as the 2x previous chrome chamber spec barrels.

We did encounter chrome lifting at the leeds (but for an allowable distance was permitted as I recall....) but they didn't give any trouble. Neither the L4 nor the L7/GPMG barrels were chromed at Enfield, but at a place in Swindon

[enfield303t]

Just got off the phone with a friend who is a Vietnam Vet, told me about 25 years ago he had a International Harvester M14 converted to semi-auto only. With open sights and younger eyes said it was easy to shoot a 1" group at 100 yards, go figure it had a chrome lined barrel. Said it was super accurate out to any distance he used it. When they made the converted M14's prohibited he got rid of it, thought with a good scope it would be as good as most bolt guns manufactured today.

[bros]

For those that claim chrome lined barrels are inherently inaccurate......you are so wrong. Maybe with yesterdays manufacturing techniques, that is not the case any more. I happen to own and shoot the proof....my Sako TRG 42 Sniper has a chrome lined bore and shoots like a laser beam. One of the most accurate "out of the box rifles I own". With handloads, sub moa all day long!!!!
I also own a AIA M10 B2 Match rifle that has that "dreaded chrome plating" and with proper handloads and on a good day I have shot sub moa groups, in spite of a terrible trigger!!!
Steve Redgwell from 303british.com whom I respect also shuns chrome lined bores in regards to accuracy........read his article on the AIA rifles regarding chromed bores. "Competitive shooters do not use chrome lined barrels period, they are not accurate", end of quote.......for article see The Mystery of Australian International Arms
I love my AIA rifle, it is a finely made specimen, the fit and finish are beautiful. Prices keep on going up here in Canada, I'd buy another in a heartbeat!!!! As a current serving Canadian Ranger I'd be proud to carry one inspite of what all the naysayers think!!!!!
Lastly chrome barrels clean up so much easier and faster than non-chrome bores.........I'll take chrome over conventional!!!!!!!!!!!!

[Peter Laidler]

I don't think anyone's saying that chrome lined barrels are inaccurate Bros - unless I am misreading the threads after quickly scanning through them again. What is being said and proven during our scientific and extensive trials is that chromes are no more accurate.

[muffett.2008]

Our Ozzie L1A1's had chromed barrels, we would constantly check for chrome lifting at the leeds.
We sectioned one strange looking wear pattern at the throat and discovered it was not the chrome lifting, but a carbonised build up of burnt teflon from the CLP we were currently using.
This caused a bit of a stir as we had replaced countless barrels supposedly for chrome lift.
A revised cleaning policy was implemented........suddenly those chrome lined barrels had an extended life.

Just dug out the EMEI.....Barrels fitted to rifles may have either a plain steel or chromium plated bore, whilst all chambers are chromium plated.

[Son]

For those that claim chrome lined barrels are inherently inaccurate......you are so wrong. Maybe with yesterdays manufacturing techniques, that is not the case any more. I happen to own and shoot the proof....my Sako TRG 42 Sniper has a chrome lined bore and shoots like a laser beam. One of the most accurate "out of the box rifles I own". With handloads, sub moa all day long!!!!
I also own a AIA M10 B2 Match rifle that has that "dreaded chrome plating" and with proper handloads and on a good day I have shot sub moa groups, in spite of a terrible trigger!!!
Steve Redgwell from 303british.com whom I respect also shuns chrome lined bores in regards to accuracy........read his article on the AIA rifles regarding chromed bores. "Competitive shooters do not use chrome lined barrels period, they are not accurate", end of quote.......for article see The Mystery of Australian International Arms
I love my AIA rifle, it is a finely made specimen, the fit and finish are beautiful. Prices keep on going up here in Canada, I'd buy another in a heartbeat!!!! As a current serving Canadian Ranger I'd be proud to carry one inspite of what all the naysayers think!!!!!
Lastly chrome barrels clean up so much easier and faster than non-chrome bores.........I'll take chrome over conventional!!!!!!!!!!!!

Unless the manufacture of the Sako TRG 42 has changed in the last couple of years, the barrel is not chrome lined, but chrome moly steel alloy. Chrome moly is a very good material for barrels as it provides added resistance to heat and wear, but still remains machinable. Unlike a Chrome coating, which once applied, cannot be suitably machined, which is why they are not inherently accurate.

I stand by my earlier comments, and will still welcome corrections....

[enfield303t]

The whole exercise for me was to show that a chrome barrel can be accurate and the statement by Redgwell was wrong and how could anyone slag a rifle they never held or shot.

The .729 group my son shot wasn't lucky, it was a accurate gun and good shooting.

It would be no different than me being a auto journalist and calling any car crappy yet never having been behind the wheel. That is the reason I did what I did.

One more thought, would 5-R rifling be better for chroming?

[Frederick303]

I would mention that in regards to accuracy, 3 shot groups really do not mean much. Yes you can get some really small groups but the issue is the variability is the size of the groups. So in 7 groups (21 shots) you could easily have a 4.5 to 1 variance, especially if the barrel is on its way out. Inaccurate barrels or barrels with a small defect show more variability, but still put in good groups at times, especially when the group size is only 3 shots.

with 5 shot groups the variance is less, on the order of 2.8~2.5 to 1. Of course very accurate barrels show little variance between shot groups, but still a 1.8 to 1 variance is not uncommon with 5 shot groups out of excellent barrels.

Said another way, it is true that an accurate barrel will uniformly put in small 3 shot groups, but 1 (or 2) 3-shot groups that are small is not definitive proof the rifle will hold that size group for all groups or a larger number of shots.


From a competitive rifle shooting point of view 10 shot groups seem to be the norm. The AMU used to say that 14 shots was a better measure, though they used the "mean radius" method of measuring groups size (R50 circle) at a distance of no less than 300M, fired from a rifle cradle. When qualifying match ammunition in the 1960s, Lack City used 270 shot aggregates, all shot out of 1 test barrel of known accuracy.

If you doubt this, try the following: under known good conditions sit down with a plotting sheet at 200 M or less on a no wind, consistent light day. Fire 21 rounds at your target plotting each and every shot so you know which is which. Go down range and you will have 7-3 shot aggregates, 4-5 shot aggregates, 2-10 shot aggregates and 1 20 shot aggregate (plus a spare). if you like you can ignore any shot called out as shooter error (AS LONG as YOU CALLED IT OUT BEFORE LOOKING AT THE TARGET though the spotting scope) and add an extra round to account for the bad shot release. Don't cheat on that, any shots disregarded must have been called out. If you called it out and it is in the general aggregate, don't cheat on that either, ignore the shot and fire another one.

Now if you drop the furthest shot out you are at ~2 sigma level of accuracy expectation (.9523 vs. .9544) for your 20 shot group.

You can see the effect of changing out a single round by changing each of the groups by going back to front instead of front to back:

i.e. 5-shot group A: shots 1 to 5, 6-10, 11-15 and 16 to 20, each form 5 shot groups, shot 21 ignored.
5 shot group B: shot 1 ignored; 2-6, 7-11, 12-16, 17-21 form 5 shot groups.

You can also test the mean radius of each of the groups. same is true of the 10 shot groups. lots of date generated with only 22 shots expended (1 shot is to make sure bore is fouled)

You will find such an exercise very illuminating, both for what is constant and what is not.

[Sentryduty]

That is quite a test battery, but I think that it is probably outside of the scope of what enfield303t was looking to demonstrate with his AIA B2.

I think it appears to perform acceptably, why overthink it? At the cost of .308 ammunition these days I would only audit the performance of a rifle barrel that seriously if it were expected to make me money.

Personally 2 MOA at 100m or better from a standard military or military pattern rifle, is good in my expectations, 3 MOA is an SKS and +4 MOA is a waste of my personal ammunition stocks.

I see nothing wrong with this B2 or the basic groups provided.

[Frederick303]

If one is going to make a statement regarding the accuracy of a rifle barrel/action/rifle and you have fired exactly 9 rounds, of which one you have disregarded....well that does not provide a very high level of confidence as to what one could reasonably expect on target afield. It is not only the size of a group of size "X", but where the group moves as the rifle heats up that matter, and shots should not be disregarded unless the shot is called out and where it is called turns out to be true. Otherwise you are simply cherry picking the results and I have seen any number of well worn rifles that would turn in a few good 3 shot (or 2 shot groups) but would not call them accurate. If 22 carefully fired rounds is considered excessive, well ammunition must be so dear that shooting as a sport is beyond the means of most men.

This rifle could be very accurate, the 8 shots out of 9 posted put in groups of 1.18, .8365 and .729 (with one shot excluded). There is nothing to say the rifle is not accurate, indeed the presumption would be with these results that it is. Using the standard mathematical models, the expectation of group size would be as follows:

5 shot group: 1.03 to 1.456"
10 shot group 1.28 to 1.81"
20 shot group 1.49 to 2.11"

source: Statistical Measures of Accuracy for Riflemen and Missile Engineers, Frank Chubb (self-published) 1990 edition

But by the same measures, because of the expected variance the above means very little. For a 5 shot group with no tendency of the center of the shots to move, the variance expected in 5 5-shot groups is around 1.8 (minimum, good rifle) to over 3 (not so good rifle or ammunition combination). With only 2 usable three shot groups @ 1.5 one simply cannot predict very much, though the results were consistent with a good shooting rifle.

So yes the results are indicative, there is more of a chance that the rifle is accurate than not, but the 22 shot/21 shot test group would give far better confidence, ability to predict where the shots would lie on a target and the method mentioned, as folks shooting it will learn something of some use. If I tell you what that is you will disregard it, as you have disregarded the prior post. Often times what is given for free is considered worthless and one must pay the price to learn something to make it part of you.

As such feel free to disregard my comments, by all means the indications are the rifle is accurate.