ohihunter2014 said:
loading 9mm for S&W m&p 4.5 inch service weapon.
What advice do you guys have to squeeze every bit of accuracy out
Of my reloads?
Are plated bullets fine? What powder? What about slugging barrel?
I want the best cause I'll be competing ... idpa
First, I would check the twist rate of your barrel as S&W changed the twist rate twice to address the inaccuracy issues of 9mm M&P barrels. They started out with 1:18 twist rate then changed it to 1:24 and it is now 1:10 (similar to Glock's 1:9.84). You can call S&W customer service to verify the twist rate of your barrel but I believe 1:10 barrels have one or two dimples on the bottom of the barrel lugs -
http://www.thehighroad.org/showthread.php?t=780301
With that said, while most aftermarket match barrels have 1:16 twist rate and Wilson Combat switched from 1:10 to 1:16, I have experienced greater accuracy from 1:20 twist rate KKM barrels compared to 1:16 Lone Wolf and 1:10 factory Glock barrels. So before considering barrel change, test some loads for accuracy to see how well your current barrel shoots as I have gotten sub 2" 25 yard groups with factory 1:10 Glock barrels and 1:20 KKM barrels using regular plated Berry's 124 gr RN and thick plated RMR HM 124 gr RN -
http://www.thehighroad.org/showthread.php?p=9924922#post9924922
If you are looking for accurate minimum power factor loads for IDPA, I would suggest the following:
- It is easier to make 125 PF with 124/147 gr bullets than 115 gr bullets as 124/147 gr will make PF with lower to mid range load data that produces accuracy with less felt recoil and muzzle flip for faster follow up shots/double taps (keep in mind that USPSA/IDPA scoring favors faster stage times so utmost bullseye match level accuracy is not paramount - and for this reason many match shooters shoot plated/coated bullets instead of jacketed)
- Lighter powder charge target loads will benefit from 124/147 gr bullets with longer bullet base than 115 gr bullets for greater neck tension which contributes to more consistent chamber pressures (that leads to more consistent muzzle velocities and lower SD) and longer bearing surface of bullet base will better engage the rifling for greater rotational stability in flight
- You can consider JHP bullets for most accurate loads as center of gravity is shifted further back towards the bullet base for greater rotational stability in flight but for action pistol matches, utmost bullseye match level accuracy is not needed and plated bullets come in JHP profiles as well (RMR sells 124/147 HM plated HP bullets)
- While using same headstamp and once-fired brass can reduce flyers which is crucial for bullseye match shooting, I don't think it's feasible or necessary for action pistol matches like IDPA that does not require bullseye match level of accuracy. I think there are reloading variables that can trump use of mixed range brass like bullet and powder selection and more consistent powder charges and bullet seating depth/less bullet setback
- Berry's bullets are sized slightly larger at .3555" (instead of .355") and produce greater neck tension while sealing tighter with the barrel. RMR HM bullets use harder 11-12 BHN alloy core for greater neck tension that minimize bullet setback. If you want greater accuracy, it's not the finished OAL but "chambered" OAL after bullet nose slams on the feed ramp that matters. Most of my RMR loads do not experience any bullet setback using .377" taper crimp.
- For lighter target loads, faster burn rate powders than W231/HP-38 are better suited than slower burn rate powders. Popular match powders are W231/HP-38, N320, Titegroup, WST, etc.
- Load to 130 PF to give you some buffer as temperature sensitivity of powders will make your loads slower in colder temperatures. Titegroup is less temperature sensitive than W231/HP-38 and powders like WST/N320/WSF are reverse temperature sensitive -
http://www.thehighroad.org/showthread.php?p=10117881#post10117881
- Consider using longer OAL/COL to reduce gas leakage. While I usually use 1.135" with 124 gr RN for general purpose range loads that must work in various pistols, I will use 1.160" to squeeze out more accuracy.
Regular plated Berry's 124 gr RN @ 25 yards with Titegroup
Thick plated RMR HM 124 gr RN @ 25 yards with WST/BE-86