Range Report Finally able to chrono factory ammo on my RPR 6.5CM

[seansmd]

Chrono data 2/23/2019 - Magnetospeed sporter
RPR 6.5MM Creedmoor, Viper PST GEN2 5x25 FFP, Area 419 brake
103y, 51 degrees, 57% Humidity, 37 Dew Point, 27.36 inHg, 27.36 BARO inHg, 2453 ft, 2549 Dens Alt.


Group #1 Center, Sellior & Bellot 140g
2681 AVG
2692 HI
2667 LOW
9 SD
25 ES

Group #2 Top Left, Hornady 147g ELD match
2662 AVG
2674 HI
2646 LOW
11 SD
28 ES

Group #3 Top Right, Hornady 140g ELD Match
2686 AVG
2693 HI
2671 LOW
9 SD
22 ES

Group #4 Bottom Left, Hornady 140g ELD Match
2688 AVG
2717 HI
2664 LOW
22 SD
53 ES

Group #5 Bottom Right, Prime 130g Match
2739 AVG
2750 HI
2725 LOW

9 SD
25 ES

I was not happy with the bench rest (caldwell the Rock) I used for this chrono data, not as stable as I expected. I do not know if the poor groups are a result of the chrono, the rest, or me in this setup, could be a combination of all three I am sure.

I then moved back to my atlas bi-pod, and rear bag on the bench with the chrono removed and shot 3 groups (top 3) of the Hornady 140g, and 2 groups (bottom 2) of the S&B.

 

[bfglowkey]

I agree and maybe its just me but when I use my Mag Sporter barrel mount chrono my groups open up. So when I load develop now I don't use the chrono on when I am checking grouping. I have mashed together a few load dev techniques into one. I only shoot with it on to gather intial data to see if I am going to pursue a load....then at the end when I have it grouping right to verify velocity etc. Makes me a happier man.

 

[Racer88]

What is most remarkable is that there is no positive correlation between "better" SDs and ESes and better groups. Rather... in this case... at this distance, we can see an INVERSE correlation.

 

[seansmd]

@Racer88 my working belief is that 100y the group differences are more my skill, or lack of skill, than the spread and deviation. Worded another way my skill SD and ES is a bigger number than the ammo. I look forward to longer distances, there I believe the better match bullets, with better SD/ES well be more consistent and tighter.

 

[Racer88]

@Racer88 my working belief is that 100y the group differences are more my skill, or lack of skill, than the spread and deviation. Worded another way my skill SD and ES is a bigger number than the ammo. I look forward to longer distances, there I believe the better match bullets, with better SD/ES well be more consistent and tighter.

I hear ya. The trick is eliminating human error... which is, of course, nearly impossible.

 

[W54/XM-388]

I hear ya. The trick is eliminating human error... which is, of course, nearly impossible.

Get a really good mechanical rest that locks in the rifle, and a good isolating remote trigger release, use a high magnification scope to an exact grid point on a target.

 

[Racer88]

Get a really good mechanical rest that locks in the rifle, and a good isolating remote trigger release, use a high magnification scope to an exact grid point on a target.

From what I've gathered, mechanical rests (like the "lead sled") have all kinds of issues when it comes to shooting groups to develop loads.

 

[W54/XM-388]

From what I've gathered, mechanical rests (like the "lead sled") have all kinds of issues when it comes to shooting groups to develop loads.

The "lead sled" is one of the cheapest and worst options.
There are much better ones that are used to very good results. They just aren't cheap.

 

[seansmd]

The "lead sled" is one of the cheapest and worst options.
There are much better ones that are used to very good results. They just aren't cheap.

I knew when I bought it, that it was cheap, I still expected it to be better than me! .

Garage sale fodder,

 

[clcustom1911]

I agree and maybe its just me but when I use my Mag Sporter barrel mount chrono my groups open up. So when I load develop now I don't use the chrono on when I am checking grouping. I have mashed together a few load dev techniques into one. I only shoot with it on to gather intial data to see if I am going to pursue a load....then at the end when I have it grouping right to verify velocity etc. Makes me a happier man.

Using a magnetospeed ALWAYS jacks with my groups. It's beautiful for muzzle velocity data, not for groups.

 

[Racer88]

Using a magnetospeed ALWAYS jacks with my groups. It's beautiful for muzzle velocity data, not for groups.

There are ways to mount the MS off the barrel. Works quite well.

 

[clcustom1911]

There are ways to mount the MS off the barrel. Works quite well.

How far off the barrel?

 

[Racer88]

How far off the barrel?

Not touching the barrel at all... mounted from a pic rail on the handguard. There are two mounts that I'm aware of... One from MK Machining. The other from Wiser Precision (?). I have the MKM.

 

[seansmd]

Not touching the barrel at all... mounted from a pic rail on the handguard. There are two mounts that I'm aware of... One from MK Machining. The other from Wiser Precision (?). I have the MKM.

Interesting, and you don't see a spread using this mounting option?
I wasn't sure if the spread was the barrel harmonics or the MS in the path of the gasses and bullet exiting the barrel.

 

[clcustom1911]

That's a sweet piece of gear. I'm a cheap-ass so, I definitely won't be buying it ??????

 

[Racer88]

Interesting, and you don't see a spread using this mounting option?
I wasn't sure if the spread was the barrel harmonics or the MS in the path of the gasses and bullet exiting the barrel.

There is definitely an effect on barrel harmonics (with SOME rifles) when it's attached to the barrel. There is no debate about that. Whether the presence of the bayonet has an effect on gasses and shockwaves leading to a change in groups is subject to debate.

I have not seen a spreading of the groups with this off-barrel mount. I'd have to do more testing to determine if there is a change in POI. Again, it's difficult to nail down if the change is ME or the gear. So, it would take a large sample size to determine a trend. I just haven't committed to testing it myself. The guys at MKM say they've tested it and found no change.