DO chase the lands!

[John Weigel]

I hope this is of interest to those shooting 'jammed' 180 VLDs with AR2209 powder. It's taken too long for me to figure this one out re throat erosion rate in SAUM barrel using 2209 powder. Until relatively recently I have used 180 Hybrids, tuning by jump distance, within bracket of 18-30 thou jump, then fine tuning with tuner. Occasionally I'd retest, and re-tune with tuner. I figured that if throat erosion meant ever-longer jumps, no problem, I can re-establish harmonic sweet spot with tuner. Then I switched to VLDs six months or so back. I shoot with three different rifles; all barrels at time of switch to VLDs looked good - fairly good groups no matter the position of tuner, given jam (not really 'jam' - 15 thousandths beyond contact with lands). Simultaneously experimenting with at least one newish barrel (first 100 rounds invested to fire-forming virgin brass - though typically this yields awesome groups), and one barrel with some use - say 500 rounds of history with Hybrids. Yet, within a hundred shots (post 100 round break in) for each established tune, groups began to open up typically from repeatable 5-shot .25MOA to more like 4MOA. So I began re-measuring shoulder to lands dimensions more often. Yikes. With my loads - approx 55 gr 2209 generating speeds for each somewhere in the 2905 -2930 fps area, with 180 VLDS with initial seating depth of -15 to -20 thous - usually -.15 ('jam' of 15 thousandths into land), and weight-sorted White River primers, the lands will recede at least 10 thousandths of an inch per 100 rounds, and as much as 20 thous per 100 rounds. I have double and triple-checked my data. I still have trouble believing it - and I don't think anyone I've spoken to about it so far has believed it. Any VLDs-into-lands-with-2209 shooters out there keep an eye on throat erosion? The good news is that I've found that if I 'chase the lands', in contravention of one of the two most sacred Cortina tenets, I can keep a sweet tune - now several barrels into the 500+ rounds of barrel life. No appreciable change in muzzle speed, though batch to batch variation in 2209 is nuts. I'm going to revisit trying AR2213sc, though my earlier trials a couple of years ago were not exactly impressive.

[willow]

10 thou per 100 rounds seems very high John, even for a SAUM. Speaking to a few who shoot this calibre, their experience typically results in the lands moving about 5 thou every 100 rounds. Both of my SAUM Improved barrels have not seen that much erosion but I'm also not pushing mine as fast simply because I start to run into pressure above 2860fps using 2209 in my Borden actions.

Do you have one of Matt Paroz's new tools on finding the lands? That tool is brilliant and gives repeatable results. I was previously using the Wheeler method and found I was seated 10-15 thou further towards the lands than where I initially thought.

[John Weigel]

Thanks for the reply Kris. I have not purchased one of Matt's 'lands guage', though he showed a prototype to me, and I was duly impressed. I plan on obtaining one. In the mean time, I use the tried and true method (popularised by Speedy and Erik C) of removing barrel, sizing dummy round in ever shorter proportion until kiss of lands has just passed. I repeat until certain- it works well, though the Matt Paroz method would be quicker. My lands erosion with 180 hybrids was much slower than I'm now experiencing, but I haven't crunched numbers - I will try to find sufficient info in my notes. Maybe there's something mechanical about the ignition while projectile is contained slightly more than when a tiny 'jump' occurs, as per traditional seating for many shooters - and perhaps the majority of those in the US. The erosion I'm experiencing has surprised me, and my next step is to try slower 2213sc and further measuring of just what the difference in ignition between CCI/Federal primers and White River. I' don't have obvious pressure issues at 2920fps, but will try going back to sub 2900 for a test with 2209 if I don't find positive result with the 13sc. Thanks again.

[ned kelly]

G'day All,
I've had very good results with a number of different cartridges by using 2 thou less than loaded round bushings , moly bullets and seating them +0.010 longer than jam.
As the bolt closes, it reseats the moly'd bullet so grip/friction/whatever is normalised round to round and it also allows the bullet to be centered. I clean with Iosso to keep the throat smooth. Its worked well with a .22BR with 80gn VLD's doing about 3200fps, 6x47lap @ 3050fps w/107 SMK, 6PPC's, .223 etc
Food for thought, hope it helps.
Cheers Geoff

[fclassNrugby]

G'day All,
I've had very good results with a number of different cartridges by using 2 thou less than loaded round bushings , moly bullets and seating them +0.010 longer than jam.
As the bolt closes, it reseats the moly'd bullet so grip/friction/whatever is normalised round to round and it also allows the bullet to be centered. I clean with Iosso to keep the throat smooth. Its worked well with a .22BR with 80gn VLD's doing about 3200fps, 6x47lap @ 3050fps w/107 SMK, 6PPC's, .223 etc
Food for thought, hope it helps.
Cheers Geoff

Hi Geoff, does the projectile not stick in the barrel if you need to extract the round without discharging it? that's the reason i do not use this method and then i get a dump of powder in the chamber. does the molly stop that stick?

[ned kelly]

G'day All,
I leave the bolt open and the round in the feed ramp ready to chamber, I'll chamber when the wind/mirage is "right" and usually fire within 5-15 seconds at most. Its never been an issue in 25 years of competition. I am fully aware of the risk and with light neck tension, the bullet isn't hard jammed and the Iosso keeps the chamber lead polished so hopefully it isn't "too grippy".
In the event of a stuck bullet, I always carry the appropriate tools to clean out the action of powder and remove stuck projectiles. If I DNF oh well my bad.
I would suggest you work out your own method, test it and see if the risk is worth it. If the accuracy isn't there then it is a moot point.
Personally, I have found the method to give consistent results as the bullet is always sitting against the rifling exactly the same as the previous one regardless of throat wear. Especially if pre loading for major events.
Alternatively, load you ammo long and at lunch time recheck your seating depth and reseat the ammo for after lunch, maybe every 2nd or 3rd range recheck and maybe a full clean the barrel.
Its about find what works and removing the processes that dont add to the accuracy for the EFFORT they entail to the point every process is ESSENTIAL for the job.
Hope this helps
Cheers Geoff

[John Weigel]

I'd genuinely like to hear from anyone else who shoots 180 VLDs with 2209 powder to vicinity of 2915 fps. What sort of rate of throat erosion have you observed? My data re big erosion with this combo is based on 5 different barrels - it's solid. Interestingly, so long as I chase the lands every 50 rounds, I'm still good to go with no adjustment to tuner. If anyone has had same or different results, properly measured and 'chased', I'd love to hear about it here or email. Confounded! JW