243Win: brass, brands, weights and velocities.

[pemo]

Greetings from Denmark

After reloading for my rifles for ~5yrs I recently reached a stage where I wanted to make a small test if I could see systematic differences in precision and muzzle velocities depending on brass brand and weight.

I had a selection of different brass for my Schultz & Larsen model "Victory" hunting rifle in 243W - http://greatdanerifles.com/. The barrel is a normal hunting barrel profile - Ø:15mm/0.6in at the muzzle. I am using a Sonic 45 suppressor and the rifle is topped with a Meopta R2 2.5-15x56 in QRW rings mounted on a picatinny rail.

All cases were "homogenized": FL sized, annealed, length trimmed, neck-turned, primer pocket reamed, flash hole deburred etc...

I weighed 90 cases of RWS (33), Norma (17), Sako (15), Lapua (12), Remington (10) og Geco (3)

Brand: Count (N) - Average(AVE) - Standard deviation (SD)

Remington: N=10 – AVE: 161,6grs – SD: 0,44
Norma: N=17 – AVE: 164,5grs – SD: 2,4
Lapua: N=12 – AVE: 172,1grs – SD: 0,90
Sako: N=15 – AVE: 171,3grs – SD: 1,6
RWS: N=33 – AVE: 180,1grs – SD: 4,6
(Geco: N=3 – AVE: 183,3grs – SD: 0,06)


HISTOGRAM EXAMPLES

I selected groups of cases for testing in 5gr intervals for testing for each brand. RWS showed a relatively large variation in weights so I selected two groups - "RWS light" and "RWS heavy" respectively.

HISTOGRAMS OF SELECTED CASE WEIGHTS

The testing load was 85grs Sierra GMK, 46grs Norma MRP powder, CCI 250, COL: 66,4mm/2.598in which shows half decent precision in this rifle. This test load is 2grs below my normal hunting load with same components.


SIX SHOT GROUP 85grs SGMK - 0,6MOA

Under the assumption that the light Remington cases have the normal 243W 54grs H2O capacity and a brass density of 8.4 g/cc, Quickload can generate a model for the velocities I could expect to measure at the range as the case capacity decreased with increasing weight of the cases.


Quickload chamber pressure/velocity as a function of brass weight (900mps=2953fps / 940mps=3084fps)

I normally hunt at distances within 200m so I first tested for precision at 100m, shooting a 5-shot group based on 158,8grs Norma, 162,2 Remington, 171,1grs Sako, 173,1grs Lapua and 183,5 Geco cases. Resulting in a 0.39moa 5 shot group, see pictures below. Apparently, precision is fine for hunting within 200m.

5-SHOTS – 5 DIFFERENT CASES
Shot 1 (Norma) centre target, 2 fouling shots lower left.

SHOT 2 (Remington)

SHOT 3 (Sako)

SHOT 4 (Lapua)

SHOT 5 (GECO + a third shot in fouling group)

RESULTS

I used a ProChrono Digital chronograph at the range and achieved the following results.

TARGETS FROM CHRONO-RANGE-SESSION (the two flyers in the RWS groups are shooter errors)

Average POI doesn't seem to change significantly in a hunting perspective at 100m.

VELOCITIES 5M FROM MUZZLE

AVERAGE BRASS WEIGHTS AND VELOCITIES (Sako & Lapua are combined, since the weights are similar)

CHRONOGRAPHED AND MODELLED (QL) VELOCITIES AS A FUNCTION OF BRASS WEIGHT

Observations / Interpretation / Conclusion

This standard barrel is faster than QL predictions.

Lowest velocity is from the lightest case (911mps / 2989fps; 161.2grs Remington)

Highest velocity is from the heaviest case (972mps / 3189fps; 183.9grs RWS)

Maximum difference in velocity of the same load in different cases is 61mps / 200fps – obviously a good argument for weight sorting cases for LR shoting as is wellknown

I will need 2.7grs more powder in the lightest case to increase the speed 200fps according to QL, and with a difference in case weight of 22.7grs it appears that 8grs of brass is roughly equivalent to 1gr of MRP powder (slow, magnum type)

I generally weigh my powder to +/- 0.1grs with my RCBS 1500 combo. It follows from the point above, that I ought to weigh my brass to +/- 0.8grs as this will have similar level of consequence on muzzle velocity.

There is a positive correlation between case weight and velocity – Heavier case -> Less volume -> Higher pressure -> Higher velocity.

Within hunting distances (<200m) there will be a max vertical difference of POI of 1.4cm / 0.55in between fastest and slowest projectile. So I conclude that mixing brass can be acceptable for hunting purposes BUT...

Pressure will of course be much different in the different cases, so loads must be developed based on the heaviest cases for obvious safety reasons.

And of course, all this is only valid for this rifle and the limited shooting distances (<200m/218yards) where I hunt.

Any comments ?



PS: please forgive any spelling and language errors...

 

[243winxb]

Good info. Ty. The weight of brass in the chamber volume makes a difference. After prep, i sort the same lot/headstamp by 3/10 gr. Makes a difference when the lot variation is 3 to 4 grs overall.

 

[K22]

You have the patience of a saint - you'd make an excellent research scientist.

 

[Zero333]

That's a fine shooting rifle to say the least.

 

[pemo]

Thanks

This rifle maker, Schultz & Larsen, might not be known to many outside Scandinavia, so here's a few snaps of what she's been up to through the years...

Set up for wild boar night hunting in Sweden. 9.3x62 Mauser barrel, 3-12 S&B Zenith

Result

Testing loads in 6.5x55SE, semi heavy barrel, 4.5-30x50 bushnell Elite 6500 Tactical

Red fox (200yds) on a frosty morning, 6.5x55SE

 

[Bigguy1951]

Great information here, thought out well. I would like to have seen the average velocities based on 10 or more shots. Three is a small sample size. Great job.

 

[pemo]

Great information here, thought out well. I would like to have seen the average velocities based on 10 or more shots. Three is a small sample size. Great job.

Absolutely right !!

I loaded 5 of each group, but weather was changing between showers and dry all the time last saturday, so I decided to go for initial results rather than a defendable sample size at first.

I will get the last two of each group chrono'ed ASAP and consider a reload/repeat of the same cases.

 

[pemo]

I measured the volume of the fired cases today using this procedure http://forum.accurateshooter.com/threads/case-volume-determination-pic-heavy.3896148/

There is a decent inverse correlation between volume and case weights, correlation coefficient 0.92.

All cases, except RWS heavy, have higher volumes than the 243W standard of 54grs water.

The picture becomes more fuzzy when plotting muzzle velocities vs case volume, but the trend is still recognizable, correlation coefficient 0.72 (trend line for all data pooled together)

 

[36Red0357]

Great work! Very interesting Information!

 

[6MMsteve]

Thanks

This rifle maker, Schultz & Larsen, might not be known to many outside Scandinavia, so here's a few snaps of what she's been up to through the years...

Set up for wild boar night hunting in Sweden. 9.3x62 Mauser barrel, 3-12 S&B Zenith

Result

Testing loads in 6.5x55SE, semi heavy barrel, 4.5-30x50 bushnell Elite 6500 Tactical

Red fox (200yds) on a frosty morning, 6.5x55SE

A buddy of mine had a heavy S&L action I tried for years to buy it, it was a heavy duty thick action and smooth this was 20 yrs ago